Green’s Dictionary of Slang

1. (UK Und., also lach) to let in.

1728		Defoe Street Robberies Considered 33: Latch, let in.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1859		Matsell Vocabulum 49: lach [sic] Let in. ‘The cove is bene, shall we lach him?’ the man is good, shall we let him in? ‘If he is not leaky.’ ‘I’ll answer for him; he is staunch.’.

2. (US black) ? to obtain, to grab.

1935

Ted Yates This Is New York 11 Oct. [synd. col.] ‘Joe Louis [...] latched himself some rails and showed all Detroit that ‘tin’ can be turned into gold .

3. (US black) to catch (up).

1937

C. Himes ‘The Night’s for Cryin’’ in Coll. Stories (1990) 133: ‘Dar’s uh green sedan up front, uh fo’ do’ job. Latch on it ‘n earn dis dime, big dime’.

4. (US) to get married.

1942

Berrey & Van den Bark Amer. Thes. Sl.

5. (US campus) to embrace.

1959

J. Farris Harrison High 104: Bart and Cootie started latching and he and Ruthie necked too [HDAS].

6. to take someone’s arm.

1957

Mad mag. Mar.–Apr. 5: Latch on, baby ... I know a dive down the street.

7. to work out, to discover.

1955

‘Bailey Morgan’ ‘Dig that Crazy Corpse’ in Pursuit Mar. (2008) 164: I regret to say you latched the rumble thoroughly.