Green’s Dictionary of Slang

1. (W.I.) one shilling (post-1969 value 10 cents) [abbr. macaroni n.¹ (3)].

1873		C. Rampini Letters from Jamaica 95: The negro nomenclature of coins is as follows: – [...] Mac (macaroni), a shilling.
1909		‘Tom Redcam’ One Brown Gal 37/1: Get you ten ‘mac’ a week and don’t fool.
1912		C. McKay ‘Cotch Donkey’ Constab Ballads 47: Ef dem summons me, / Mek me pay few mac.
1929		M. Beckwith Black Roadways 49: The following names [...] still in use today: Bit, 4½d. or 9 cents. Four bits, 1s. 6d. or 36 cents. Mac-and-thruppence, 1s. 3d. or 30 cents. Quattie, 1½d. or 3 cents. Gill, 3 farthings or 1½ cents.
1942		L. Bennett ‘Jamaica Patoah’ in Jamaica Dialect Verses 1: An’ some oder tings wat come up / To mack-an-tuppy in all.
1966		(ref. to 1940s) L. Bennett Jamaica Labrish 223: mack-an-tup. one shilling and a penny ha’penny.

2. a condom [abbr. SE mac(intosh)].

1979		‘Baker’s Boy’ in Bold (1979) 11: So if you meet a maiden fair / And self-control you lack, / Before you have your rub-a-dub-dub / Be sure you wear a mac.
1999		(con. 1979–80) A. Wheatle Brixton Rock (2004) 171: It wouldn’t have looked all that good if me and you were chatting and all of a sudden, I pulled out a mac.

3. see mack n.²