Green’s Dictionary of Slang

cool adv.

1. (also coolly) calmly, in an unruffled manner.

[[UK]T. Shadwell Squire of Alsatia III i: I’ll talk with him cool in a morning first; perhaps I may redeem him].
[UK]R.B. Peake Americans Abroad II iv: My madeira! – ha! ha! cool!
[US]T. Haliburton Clockmaker I 255: I bit in my breath, and spoke quite cool.
[Aus]Bell’s Life in Sydney 20 Nov. 3/2: That’s a nice young gal [i.e. a prostitute], I reckon; I calculate I’ll splice her cool; get change for these coins.
[UK]G.A. Sala Quite Alone I 119: I will keep my head cool, and won’t touch ivory to-night.
[Aus]H. Lawson ‘Stiffner and Jim’ in Roderick (1972) 127: He took it all pretty cool.
[UK]Boy’s Own Paper 15 Dec. 164: Fancy coolly staying upstairs smoking, instead of coming into prep!
[UK]‘Sapper’ Female of the Species (1961) 39: The car must have been cooly stolen from his garage.
[US](con. 1948) G. Mandel Flee the Angry Strangers 19: I want to get my boy and live cool.
[UK]T. Keyes All Night Stand 41: I took all this very cool. ‘I don’t know what you’re on at.’.
[UK]T. Paulin ‘Waftage: An Irregular Ode’ in Fivemiletown 8: So, real cool, I growled / ‘Lady, no way you’ll walk / right over me’ / Dead on. I chucked her then.
[UK]Guardian Guide 26 June–2 July 5: His accountant had coolly pilfered around £6 million.
[US]N. Hopkinson Midnight Robber 60: Antonio stopped him cool-cool.

2. askance, suspiciously.

[UK]Sporting Mag. Nov. XVII 90/2: Nor did he ever look cool, / even upon his enemies.
[Aus]‘Rolf Boldrewood’ Robbery Under Arms (1922) 53: I had begun to think the fellows looked a little cool on us the last three or four nights, as our losses were growing big.

3. (US black) very.

[UK]A. Salkey Late Emancipation of Jerry Stover (1982) 181: This Kirby look cool bad. Black like me, too. Could always be a brother o’ mine.

In phrases

play it cool (v.) (also play cool, pluck it cool)

(orig. US black) to act in an uninterested or disinterested manner, to control every emotion.

Hal Ellson Duke 3: That’s the way I dig it. I do it nice. Play it cool.
[US]Laurents & Sondheim West Side Story I vi: Go man, go, [...] Just play it cool, boy.
[UK]R. Cook Crust on its Uppers 98: You just can’t play it too cool.
[UK]A. Salkey Late Emancipation of Jerry Stover (1982) 20: Got to pluck it cool.
[US]N. Heard Howard Street 39: Now he was playing cool, posing for the crowd.
[UK]J. Rosenthal Spend, Spend, Spend Scene 60: I played it cool when I saw him. Hard to get. I played it cool for – oh – nearly twenty minutes ...
[US]T. Wolfe Bonfire of the Vanities 377: Why did I have to play it so cool with the woman?
[UK]I. Welsh Filth 21: Best to play it cool and let their anger ferment for a bit.
[UK]Indep. on Sun. Culture 30 Jan. 12: He is so hot it is like UNBELIEVABLE – but I play it cool.
[Aus]N. Cummins Tales of the Honey Badger [ebook] We’ll play it cool. Sneak up on the pricks real quiet and then smash ’em.
take it cool (v.) (also take it coolly)

to relax, to remain undisturbed by events.

[UK]W.J. Neale Paul Periwinkle 524: D--n me, that’s what I call taking it cool.
[US]‘Ned Buntline’ G’hals of N.Y. 17: Do you want me ter lay off and take it cool, while we’re all a-starvin’?
[UK]F. Smedley Harry Coverdale’s Courtship 371: Gently there – take it coolly!
[UK]Wild Boys of London I 45/2: You take it coolly for a first cove.
[Aus]Bulletin (Sydney) 8 Dec. 29/4: ‘The Devil she has!’ Johnson answered, languidly. ‘Them Chows has a great fancy for big woman.’ / ‘Hum!’ said Ebenezer, ‘you take it pretty cool. If it was my old woman, I’d break that heathen’s skull for him.’.
[US]‘O. Henry’ ‘The Shocks of Doom’ in Voice of the City (1915) 101: ‘You take it cool,’ said Ide, ‘if you’ve told it to me straight.’.
[US]G. Bronson-Howard God’s Man 361: You take it cool, I’m a son-of-a-gun if you don’t.
[Can]R. Caron Go-Boy! 259: Hang tough, Roger . . . take it cool man.