The phrase in full fig means smartly dressed.
In this phrase, fig is not the noun denoting the fruit of the fig-tree (Ficus carica), but is from the verb fig, followed by out or up, meaning to smarten up, to dress up.
The verb fig is in turn probably an alteration of the verb feague, of uncertain origin, meaning to make (a horse) lively. This seems to be supported by the following three texts:
1-: This definition of the verb feague from A Classical Dictionary of the Vulgar Tongue (London: S. Hooper, 1785), by the English antiquary and lexicographer Francis Grose (1731-1791):
FEAGUE, to feague a horse, to put ginger up a horse’s fundament, to make him lively and carry his tail well; it is said, a forfeit is incurred by any horse dealer’s servant who shall show a horse without first feagueing him, used figuratively for encouraging or spiriting one up.
2-: This extract from the account of an action brought in the Court of Common Pleas, Westminster, London, to recover the money paid for a horse, published in The Sporting Magazine; or, Monthly Calendar of the Transactions of the Turf, the Chase, and every other Diversion interesting to the Man of Pleasure, Enterprize & Spirit (London, England) of July 1810:
Stephen Ledyard, horse-dealer, stated, that the horse was offered to him for sale at the fair, but he would not have any thing to do with him, as his eyes were hollow, sunk, and blue, which shewed that he was diseased.
On his cross-examination, he said the horse appeared lively, but he was figged with ginger.
3-: This extract from Tom Crib’s Memorial to Congress. With a Preface, Notes, and Appendix (London: Printed for Longman, Hurst, Rees, Orme, and Brown, 1819), by the Irish author Thomas Moore (1779-1852)—the author parodies the Aix-la-Chapelle diplomatic conference, between Britain and her then allies, through the guise of a boxing match:
Poor Georgy was done up in no time at all,
And his spunkiest backers were forc’d to sing small. †
In vain did they try to fig up the old lad,
’Twas like using persuaders ‡ upon a dead prad; §
† To be humbled or abashed. ‡ Spurs. § Horse.
The earliest occurrences of the phrase figged out, meaning dressed up, that I have found are as follows, in chronological order:
1-: From an unsigned letter from India, dated Cawnpore, Friday 4th April 1817, published in The Globe (London, England) of Friday 29th May 1818—in the following, the author, a British serviceman, describes the Nawab Vizier during an informal meal at his palace in Lucknow, in India:
His dress was made up of the richest and most costly shawls, trimmed with gold lace and sable; his turban ornamented with a beautiful emerald of immense size, surmounted with a crescent of fine diamonds, and in its folds were entwined strings of very valuable pearls; yet, not withstanding all this finery, I was told that my gentleman was in his undress: on state occasions he sports jewels worth two millions sterling. I must confess, I should like to meet him on a dark night properly figged out, I should certainly try to prevail on him to part with a little of his finery; for it is really a bore that we gentlemen, with white faces, should be so hard pushed to raise the wind, whilst people as black as my boot are wallowing in riches.
2-: From Isn’t it Odd? (London: Printed for G. and W. B. Whittaker, 1822), by ‘Marmaduke Merrywhistle’:
I […] walked over to—Erasmus Fubbs—I saw him through the window—he did not see me—“and now,” thinks I, “a Rowland for an Oliver, Master Fubbs.” I went to a house of entertainment close by, to plan my stratagem; for I had digested nothing, as my effecting any trick would depend upon whether I got a good opportunity, and how it was to be got; I wished not be seen, nor suspected of it, if possible. I understood, accidentally through the waiter, that there was a club held at the house, of which Fubbs was a member; that that was club-night, and also his night for being president; on this foundation I planned my trick; I went out and bought some of those trifling fireworks called crackers, which go off with reiterated bounces; and returning to the house, from a retired room, saw the members of the club assemble; and at last Fubbs, figged out in style and his wig full powdered: through bribing the waiter I got two crackers affixed to Fubbs’ skirts and one to his wig, when he was in the chair.
The earliest occurrences of the phrase in full fig that I have found are as follows, in chronological order:
1-: From a letter to the Editor, titled Military Rank!!!, by ‘Achille, Victor, Hector, Alexander, Hyderali, Cochon Le Coque’, published in The Sun (London, England) of Monday 17th July 1820:
The young gentlemen went on shore, and going to see the garrison parade, they recognized their friend the Major in full fig.
2-: From The Drawing-Room, by ‘X. X.’, published in The Morning Post (London, England) of Wednesday 9th May 1821:
Here “Guardsmen,” cover’d o’er with lace,
There “Liners,” in a plainer case,
With “bold Dragoons,” whose whiskers fierce,
A foe’s—or female heart can pierce;
And spurs, that play destructive pranks
In ladies’ trains, or horses’ flanks.
Here Sailors, cast upon dry ground,
Their “jackets blue” with “iron bound,”
With Judges grave, in gown and wig,
Physicians—Parsons, in full fig;
With divers Quidnuncs, members all
Of the professions liberal:
While others, who’re in neither, come,
Arrayed “en bourgeois Gentilhomme.”
3-: From the following poem, published in The Literary Gazette, and Journal of Belles Lettres, Arts, Sciences, &c. (London, England) of Saturday 2nd March 1822:
VALENTINE FOR ——
Unfeeling Swain,
That hast in twain
My tender heart disjointed,
Hear now the moans,
The sighs and groans,
Of a Lass disappointed.When in my shop
Oft you would pop
To buy a bun or cheesecake,
Why did your eyes
Tell such sweet lies,
And lead me into mistake?Why in full fig
With well curl’d wig,
Ah, poor defenceless Maid!
Were to my view,
Instead of two,
Four * brilliant orbs display’d?[&c.]
London, 14th Feb. 1822.
* Viz. two eyes and two spectacle glasses.
4-: From the ‘stage directions’, at the very beginning of Noctes Ambrosianæ. No. III, published in Blackwood’s Edinburgh Magazine (Edinburgh, Midlothian, Scotland) of May 1822:
SCENE FIRST.
Time—Six o’clock, P. M. Scene—The Blue Parlour.
To Mr North, standing in the centre of the room, in full fig, Enter Mr Timothy Tickler.
word histories 
I would have assumed that “fig” in this context was short for “figure” (along the lines of saying something like “he was a fine figure of a man”). Thanks for the explanation of “feague” and the illustrative quotes showing the phrase used in context.
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Thank you.
I was aware of this hypothesis (i.e., that “fig” in this context is short for “figure”), but I have not mentioned it, because no evidence supports it.
In fact, all the evidence suggests that the noun “fig” is from the verb “fig”, variant of “feague”.
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