Green’s Dictionary of Slang

1. (US, latterly gay) any form of hat.

1900		P. White West End 404: We must remember that to superintend the distribution of socks and ‘Tams’ (she called them Tams) was a good deal more onerous.
1936		K. Mackenzie Living Rough 103: A blue tam stuck at a jaunty angle on her head.
1972		B. Rodgers Queens’ Vernacular 194: tam (fr tam o’shanter) any cap or hat.

2. (W.I. Rasta) the large woollen hat used by Rastafarians to cover their dreadlocks.

1967		(con. 1954) Babs Gonzales I Paid My Dues 92: We all wore ‘tams’ on stage.
1978		D. Hebdige Subculture 35: The colours of the Ethiopean flag emblazoned on items as various as badges [...] tams (woollen hats), walking sticks. [Ibid.] 43: The pork-pie hat disappeared to be replaced by the roughly woven ‘tam.’.
2006		R. Antoni Carnival 120: The rasta raised his eyebrows, adjusting his tam, studying the bill.