foolish or fanciful talk, ideas, plans, etc.
It is a shortening of moonshine in the water, meaning appearance without substance, something unsubstantial or unreal. In this phrase, moonshine means moonlight.
The 15th-century correspondence between members of the Paston family of Norfolk gentry, and with others connected with them in England, provides precious information about that period’s social history, politics and language, both within East Anglia and nationally.
The phrase moonshine in the water is first recorded in a letter written to John Paston on 28th October 1468:
If Syr Thomas Howys wer handelyd by Maistir Tressam [and] made byleve and put in hope of the moone shone in the water and I wot nat what, that such labour wer made that eythir he shulde be a pope or els in dyspeyr to be depryved ‘de omni beneficio ecclesiastico’ for symony, lechory, periory, and doubble variable pevyshnesse, and for admynystryng wythout auctoryté…
If Sir Thomas Howis were handled by Master Tressam and made believe and put in hope of the moonshine in the water and I don’t know what, that such labour were made that either he should be a pope or else in despair to be deprived of all benefit of clergy for simony, lechery, perjury and double variable malignity (?), and for administering without authority…
(The fact that the author of the letter didn’t feel the need to explain the phrase shows that it was already well established.)
In his textbook Lesclarcissement de la langue francoyse (1530), the teacher and scholar of languages John Palsgrave (died 1554) translated ― rather poetically ― for moone shyne in the water as pour vne chose de riens and pour vng beau neant, meaning for a thing (made up) of nothing and for a beautiful nothingness.
In Love’s Labour’s Lost, written in the mid-1590s, the English poet and playwright William Shakespeare (1564-1616) played with metaphorical meanings of moon:
(Quarto 1, 1598)
– Biron: Vouchsafe to shew the sunshine of your face,
That we (like sauages) may worship it.
– Rosaline: My face is but a Moone, and clouded too.
– King: Blessed are cloudes, to do as such cloudes do.
Vouchsafe bright Moone, and these thy Starrs to shine,
(Those cloudes remooued) vpon our waterie eyne.
– Rosaline: O vaine peticioner, begg a greater matter,
Thou now requests but Mooneshine in the water.
A dish consisting of egg yolks on a sweet base, popular in the 16th and 17th centuries, was called eggs in moonshine. The term was sometimes used synonymously with moonshine in the water, as in this passage from A discourse of a discouerie for a new passage to Cataia (1576) by the English explorer and soldier Sir Humphrey Gilbert (1537-83):
It is to be intended that the King of Portingal, would not haue giuen to the Emperour, such summes of money for egges in mooneshine.
Moonshine was also the name of various sweet, usually light puddings, often made of blancmange, meringue, etc. They were originally sometimes formed in moon-shaped moulds. For instance, in The Art of Cookery, made plain and easy by the English writer on cookery and costumier Hannah Glasse (1708-70), the recipe thus begins:
First have a Piece of Tin, made in the Shape of a Half-Moon, as deep as a Half-pint Bason [= basin], and one in the Shape of a large Star, and two or three lesser ones.
In the USA, the cowboy’s food included moonshine ― white rice slow-cooked with sweet raisins.
Moonshine in the sense of smuggled or illicitly distilled alcoholic liquor appeared in the late 18th century. It was first defined by the English antiquary and lexicographer Francis Grose (1731-91) in A Classical Dictionary of the Vulgar Tongue (London, 1785):
Moonshine, a matter, or mouthful of moonshine, a trifle, nothing; the white brandy smuggled on the coasts of Kent and Sussex, is also called moonshine.
Such liquor was so named because it was smuggled at night.