A Grammatical Dictionary of Botanical Latin

birettiform, square in cross section and shallowly convex at the top, as a Roman Catholic cleric's hat (Kiger & Porter 2001): birettiformis,-e (adj.B).

NOTE: the biretta, berretta or beretta, from berret, ‘cap,’ from Late Latin birrus, ‘cloak with a hood, of Celt origin’ (WIII), “a square head covering worn by ecclesiastics that has three or four projections above the crown, often with a tassel at the top, and is red, purple, or black to correspond to the rank of cardinal, bishop, or priest” (WIII). In classical Latin, the birrus,-i (s.m.II) or birrum,-i (s.m.II) was “a cloak to keep off rains (made of silk or wool” and of a yellow color (Lewis & Short). In Greek the byrros (or birros) is a kind of cloak (=Lat. birrus), otherwise, a byrros = the kantharos, a dung-beetle, a kind of boat, a sort of drinking-cup, the black sea-bream (Liddell & Scott).