n. & v.
n. 1 a bar with a catch and lever used as a fastening for a gate etc. 2 a spring-lock preventing a door from being opened from the outside without a key after being shut.
v.tr. & intr. fasten or be fastened with a latch. latch on (often foll. by to) colloq. 1 attach oneself (to). 2 understand. on the latch fastened by the latch only, not locked.
[ prob. f. (now dial.) latch (v.) seize f. OE lccan f. Gmc ]