Green’s Dictionary of Slang

1. a piece of information, esp. concerning criminal activity, also attrib.

1901		J. Flynt World of Graft 164: ‘So much down now,’ he said, ‘and so much when the show’s over. Otherwise it’s a tip-off and pinch.’ .
1917		Van Loan ‘The Last Chance’ in Old Man Curry 99: That’s the tip-off; when a souse won’t listen to your gentle voice, it’s time [etc.].
1923		H.C. Witwer Fighting Blood 241: I thank Spence for the tip-off.
1938		J. Curtis They Drive by Night 67: His release from stir corresponds and his pal gives us the tip-off.
1949		R. Chandler Little Sister 150: Why was he in hock? Tipoff that he was who he was.
1959		J. Thompson Getaway in Four Novels (1983) 45: Then there’s the livestock — that’s the real tip-off.
1961		J. Sparks Burglar to the Nobility 136: Someone had really been signing. A proper tip-off all round.
1964		H.S. Thompson letter 29 Jan. in Proud Highway (1997) 435: The real tip-off came when you said, ‘All we have to worry about is the nervous ones [...].’.
1972		G.V. Higgins Friends of Eddie Coyle 18: One of the screws saw him getting chummy with the chaplain [...] which is usually the tip-off.
1983		S. Gee Never in My Lifetime in Best Radio Plays (1984) 63: Your lot had us out, last Tuesday. Two in the morning. A tip-off.
1990		S. Morgan Homeboy 29: Such tipoffs are going to get scarcer than hen’s teeth.
1993		G. Disher Deathdeal [ebook] ‘It’s an inside tip-off’.
2000		Indep. on Sun. 16 Jan. 17: The Gay and Lesbian switchboard received a tip-off about a body near a golf course.
2009		L. McIlvanney All the Colours 27: ‘I can maybe get you something. A tip-off fee’.
2010		K. Richards Life 12: He would get a tip-off if the police were planning a bust.
2021		Breen & Conlon Hitmen 13: [F]ollowing a tip-off [gardaí] raided a small shed.
2021		P. Papathanasiou Stoning 112: ‘We asked residents for tip-offs [...] got nothin’’.
2022		A. Parks May God Forgive 32: ‘Seems they raided a flat in Roystonhill. Had a tip-off, I think’.

2. (also tip off man) an informer, an ‘inside man’.

1941		V. Davis Phenomena in Crime 64: ‘Tip-offs’ [...] divulge information leading up to crimes.
1970		‘Red’ Rudensky Gonif 95: We’ll need [...] insiders, tip-off men, whisky experts and all the luck on the planet.

3. the trigger for action.

1955

‘Hal Ellson’ Rock 125: That’s the tip-off. Ramon flipped his top.