subs. (venery).An abbreviation of FRENCH LETTER (q.v.).
LETTER-IN-THE-POST-OFFICE. See FLAG.
TO GO ON THE LETTER Q, verb. phr. (old).See quot.
1819. J. H. VAUX, Memoirs, p. 185, s.v. LETTER Q, the mace or billiard slum, is sometimes called going on the Q, or the letter Q, alluding to an instrument used in playing billiards.