Thanks, Brendan!
I just found a Chambers online, and sure enough, the last two letters of 7D mean "cheat" (colloq.) in definition 14. Had no idea.
(But I've been doing mainly U.S. barred puzzles since 1976 and had not encountered that usage until now. Except for a year when I tackled Listener puzzles, always armed with my 1994 Chambers, which is no longer with me.)