The noun honeymoon designates the holiday spent together by a newly married couple, before settling down at home.

But, originally, this noun designated the period of time following a wedding, and arose from the comparison of the mutual affection of newly-married persons to the changing moon, which is no sooner full than it begins to wane—as is clear from the following definition from Glossographia: Or a Dictionary Interpreting all such Hard Words, Whether Hebrew, Greek, Latin, Italian, Spanish, French, Teutonick, Belgick, British or Saxon, as are now used in our refined English Tongue […] (London: Thomas Newcomb, 1656), by the English lexicographer Thomas Blount (1618-1679):

hony-moon, applyed to those marryed persons that love well at first, and decline in affection afterwards; it is hony now, but it will change as the Moon.

The noun honeymoon is first recorded in A dialogue conteinyng the nomber in effect of all the prouerbes in the englishe tongue compacte in a matter concernyng two maner of mariages, made and set foorth by Iohn̄ Heywood (London: Thomas Berthelet, 1546), by the English playwright and epigrammatist John Heywood (circa 1496-circa 1578):

This yong poore couple […]
[…] The daie of weddyng and after, a while,
Could not loke eche on other, but they must smile.
As a whelpe for wantonnes in and out whipps,
So plaied these tweyne, as mery as thre chipps.
Ye there was god (quoth he) whan all is doone.
Abyde (quoth I) it was yet but hony moone.
The blacke oxe had not trode on his nor her foote. ¹
But er this branche of blys coulde reache any roote,
The floures so faded, that in fiftene weekes,
A man myght espie the chaunge in the cheekes,
Both of this pore wretch, & his wife this pore wenche.
Their faces told toies ², y^e Totnam was turnd frenche ³
And all their light laughyng turnd and translated
Into sad syghyng, all myrth was amated.
     in contemporary English:
This young poor couple […]
The day of wedding and after a while,
Could not look each on other, but they must smile.
As a whelp, for wantonness in and out whips,
So played these twain, as merry as three chips.
Yea, there was God (quoth he) when all is done.
Abide (quoth I) it was yet but honey moon.
The black ox had not trodden on his nor her foot. ¹
But ere this branch of bliss could reach any root,
The flowers so faded, that in fifteen weeks,
A man might espy the change in the cheeks,
Both of this poor wretch, and his wife this poor wench.
Their faces told toys ², that Tottenham was turned French ³
And all their light laughing turned and translated
Into sad sighing, all mirth was amated.

¹ Chiefly used in the black ox has trod on somebody’s foot and variants, the black ox denotes adversity, hardship, misfortune, also the cares of life.
² Here, the noun toy seems to denote a dislike, an aversion.
³ Tottenham is turned French is a proverb used in reference to any unlikely or remarkable change. It takes its origin from the migration of a number of French workmen to Tottenham early in the reign (1509-1547) of Henry VIII. Their competition provoked the jealousy of English workmen, and resulted in disturbances in the streets of London on May Day 1517.

The noun honeymoon then occurs in the English-Latin lexicon Abecedarium Anglico Latinum, Pro Tyrunculis Richardo Hulœto Excriptore (London: William Riddell, 1552), by Richard Huloet (of whom very little is known):

hony mone, a terme prouerbially applied to such as be newe maried, whiche wyll not fall out at the fyrste, but thone loueth the other at the beginnynge excedyngly, the likelihode of theyr exceadynge loue, appearing to aswage, y^e which time the vulgar people cal the hony mone. Aphrodisia, feriæ, hymenæ.

The following is from Cornu-copiæ, Pasquils Night cap: or, Antidot for the Head-ache (London: Printed for Thomas Thorp, 1612), by the English author Nicholas Breton (1545?-1626?):

The Iouiall time of pastime and content,
Which married persons do in kissing spend,
Was scarce begun, when all their merriment
By meanes of forked fortune mad an end.
And now their Hony-Moone, that late was cleare,
Did pale, obscure, and tenebrous appeare.

The English poet Alicia D’Anvers (née Clarke – baptised 1668-died 1725) elaborated on honeymoon in The Oxford-Act: A Poem (London: Printed for Randal Taylor, 1693):

Since then, Confusion on Confusion,
All Chaos till the Revolution;
Till a New World rose from black Billows,
And Surges roll’d as soft as Pillows.
Yet then Fate had so long been thwarting,
So stunn’d with the old Blows of Fortune,
The Aged Matron did appear,
She scarce got Breath in Four long Year:
But now recover’d brisk and Bonny,
As Bridegroom’s self, in Moon-call’d-Hony.

The noun honeymoon came to designate the first month after marriage, as explained by the English lexicographer Samuel Johnson (1709-1784) in A Dictionary of the English Language: In which the Words are deduced from their Originals, and Illustrated in their Different Significations by Examples from the best Writers. To which are Prefixed, a History of the Language, and an English Grammar (London: Printed by W. Strahan, For J. and P. Knapton; T. and T. Longman; C. Hitch and L. Hawes; A. Millar; and R. and J. Dodsley – 1755):

Honey-moon. n. s. [honey and moon] The first month after marriage, when there is nothing but tenderness and pleasure.

The acceptation the first month after marriage of honeymoon gave rise to the term honey-month, first recorded in The History of the Life, Reign, and Death of Edward II. King of England, and Lord of Ireland. With the Rise and Fall of his great Favourites, Gaveston and the Spencers. Written by E. F. in the year 1627. And Printed verbatim from the Original (London: Printed by F. C. for Charles Harper … Samuel Crouch … and Thomas Fox …, 1680):

The young King troubled at his Oath.
The sad Restrictions of his dying Father, so contrarious to his aims, trouble his unquiet thoughts; where the Idea of his absent love did hold so firm a footing. With ease he can dispence with his own engagement; but fears the Lords, whom he conceits too firmly fixt to waver. He dares not Communicate the depth of his Resolution, being a secret of too great weight to be divulged; he thinks intreaty an act too much beneath him; and to attempt at random, full of hazard. In these his restless passions, he out-runs the Honey-month of his Empire; looking asquint upon the necessary Actions of State, that requir’d his more vigilant care and foresight.

The term honey-month also occurs in Ar’t asleepe Husband? A Boulster Lecture; Stored With all variety of witty jeasts, merry Tales, and other pleasant passages; Extracted, From the choicest flowers of Philosophy, Poesy, antient and moderne History. Illustrated with Examples of incomparable constancy, in the excellent History of Philocles and Doriclea. By Philogenes Panedonius (London: Printed by R. Bishop, for R. B. or his assignes, 1640), by the English author Richard Brathwait (circa 1588-1673):

A poor State that begets pride! An undeserving honour, that moulds in the owner a supercilious aspect; a difficulty of accesse; a phantastick circular gate; and a surly uncivile speech! Weake habilliments of honour! But farre weaker Supports to beare that Colosse of honour up, if he should decline.
I have observed an excellent temperature in this kinde, in many of our Ladies: whose pleasing countenance, & affable salutes freed them of that censure which those disdainefull women worthily incurre, who hold it the best posture of State to dis-value those they consort with: and as those, who are transported with an opinion of their owne worth censure nothing worthy hearing, but what their selecter judgements approve. Dainty Idols to doate upon! These had need furnish themselves of witty Husbands; or the Honey-month will be soone done with them.

Very early, honeymoon came to be used figuratively in the sense of an initial period of enthusiasm or goodwill. This is first recorded in The discouerie of a gaping gulf vvhereinto England is like to be swallovved by another French mariage, if the Lord forbid not the banes, by letting her Maiestie see the sin and punishment thereof (London: Printed by H. Singleton for W. Page, 1579), by the English religious writer John Stubbs (circa 1541-1590):

Alas poore men, how vainely they gape at french promises, with losse of theyr Englishe possessions: If they should haue theyr desire, it vvold not be long before theyr tongues would make theyr harts ake. It might be honiemoone awhile with them but aftervvard french would be no deinty dish.

This figurative sense is also recorded in Euphues and his England, Containing his voyage and aduentures, myxed with sundrie pretie discourses of honest Loue, the discription of the countrey, the Court, and the manners of that Isle. […] (London: Printed for Gabriel Cawood, 1580), by the English author John Lyly (circa 1553-1606):

Being of the age of xx. yeares, ther was no trade or kinde of life that either fitted my humour, or serued my tourne, but the Court: thinking that place the only meanes to climbe high and fit sure. Where-in I followed the vayne of young Souldiours, who iudge nothing swéeter then warre till they féele the weight, I was there enterteined as wel by the great friends my father made, as by mine own forwardnes, wher it béeing now but Honny moone I endeuoured to Courte it with a grace.