Green’s Dictionary of Slang

1. to ‘let fly’, to let go, esp. with great energy and force.

1865		W. Hilleary diary 20 Apr. in A Webfoot Volunteer (1965) 44: The officers of Co. B. drill their men in the manual of arms while ours choose rather to ‘let us rip’.
1899		‘Steele Rudd’ On Our Selection (1953) 24: Thought you had decided to let them rip?
1900		Bulletin (Sydney) 17 Mar. 32/2: He let the old girl [horse] rip for all that she was worth.
1929		J.B. Priestley Good Companions 332: Quietly at first, then louder, louder, then letting it rip.
1938		F. Durbridge Send for Paul Temple (1992) 258: But as soon as I get back to the car, let it rip!
1949		H. Miller Sexus (1969) 36: Life is here now, any time you say the word, any time you let rip.
1951		Cusack & James Come in Spinner (1960) 103: Come, shall we let it rip?
1968		(con. 1940s) J. Healy Death of an Irish Town 31: Bernie Commons came into Charlestown on Fair and Market Day and let rip with fiery speeches which ‘the rager shams’ loved.
1978		F. Norman Dead Butler Caper 146: Then he drew in a lung-full of air and let rip with an avalanche of raw deeds.
1991		B. Hamper Rivethead (1992) 80: He was way overdue. There would be no better occasion. Let it rip!
1992		M. Coleman Fatty 295: [of breaking wind] Big Sammy [...] let rip with one that had the oxygen masks falling from the seats and tears pouring out of many pairs of eyes.
1997		C. Newland Scholar 317: She sniffed the air then, wanting to say her piece, dismissed the odour and let rip.
2000		Guardian G2 27 Mar. 8: You can let rip on the coast road.
2005		M.B. ‘Chopper’ Read Chopper 4 220: The crims let rip, so the cops let rip.

2. attrib. use of sense 1.

1900

Bulletin (Sydney) 13 Jan. 7/4: The usual happy-go-lucky, let-it-rip style of doing things was, the other day, responsible for another man’s death in Melbourne.