Green’s Dictionary of Slang

fit adj.

[note agricultural use fit, of fruits and vegetables, ready to pick, full-grown, though not necessarily fully ripe; note Shakespearian use fit, of a woman, having an aptitude for love-making]

1. very well, healthy, usu. in response to the query ‘How are you?’.

[UK]Farmer & Henley Sl. and Its Analogues.
[US]H. Blossom Checkers 56: You don’t look very fit.

2. (later 20C+ use is chiefly UK black) good-looking, attractive.

[UK]H. Smart Post to Finish I 26: Blame me, I do know whether they’re turned out all right when I see ’em, and mean my girl to look as fit as any of ’em.
[US]Dos Passos Manhattan Transfer 220: ‘She was like a wild rose [...] fresh and pink and full of the Irish and now she’s a rather stumpy businesslike looking little woman.’ ‘And you’re as fit as ever you were.’.
[UK]V. Headley Yardie 79: Dat girl yah fit, you know.
[UK](con. 1979–80) A. Wheatle Brixton Rock (2004) 27: Brenton had lost count of the number of fit girls who phoned his hostel-mate.
[US]A. Swartz ‘Sweet, Tight and Hella Stupid’ in S.F. University High School Update Mar.–Apr. 2: fit – attractive or beautiful.
[UK]J.J. Connolly Viva La Madness 35: Fit girls in their sky-blue and white CBB uniforms.
[UK]A. Wheatle Crongton Knights 19: ‘You always go on too hungry around fit girls’.

In compounds

fit-batty (adj.)

(UK black) very attractive.

[UK]A. Wheatle Dirty South 21: We could be driving convertibles [...] riding with fit-batty chicks.

SE in slang uses

In phrases

fit as a buck rat (adj.)

(N.Z.) extremely healthy.

[NZ]J. Henderson Gunner Inglorious (1974) 19: Grimy as a sweep, greasy as a butcher’s pup manhandling ammunition, but oh I feel fine, fit as a buck rat.
[NZ]G. Slatter Pagan Game (1969) 172: Fit as a buck rat.
D. Davin Salamander and the Fire 6: Anyway it was a time when the chaps were so randy – death and the desert had something to do with it. I expect, and being young and fit as buck rats [DNZE].
[NZ]N.Z. Herald 14 July 🌐 We are expecting their secret weapon to be assistant Kiwi coach Graeme Norton who is still as fit as a buck rat.
fit as a fiddle (adj.) (also fit as a fiddler)

(Aus.) extremely healthy.

[NZ]Carruthers letter in Phillips, Boyack & Malone Great Adventure (1988) 20 Mar. 260: I will be out of bed in a day or two now and am feeling fit as a fiddle.
[Aus]Baker Popular Dict. Aus. Sl.
[UK]Partridge DSUE (8th edn).
Kentucky Post 7 June [headline] Injured champion musician hopes he is fit as a fiddler.
[US] 1 Aug. 🌐 [headline] Fit as a fiddler.
fit as a trout (adj.)

(Aus./N.Z.) very healthy.

[Aus]W. Dick Bunch of Ratbags 223: Anyone would reckon he’d be fit as a trout. Fancy getting bloody T.B. at his age.
[NZ]L. Leland Kiwi-Yankee Dict. 40: ‘Old Sam is as fit as a trout, he walked five miles yesterday just to sink a few with me.’ Old Sam is in good shape.