frightener, n. — Green’s Dictionary of Slang

frightener n.

1. (also frighteners, fright(s)) threats, violence, anything that will terrify a given person into doing what is required.

1959		see put the frighteners on
1995		B. James Detective is Dead (1996) 54: ‘We’ve been doing the Smith and Wesson 645,’ Amy told him. ‘This is a real frightener.’.
2002		J. Cameron Hell on Hoe Street 176: ‘Try to shoot you.’ ‘Maybe get in a few frighteners first.’.

2. a thug, esp. as used by gangsters, casino-owners etc. to commit violence for them.

1962		R. Cook Crust on its Uppers 41: In comes Chas the frightener.
1985		S. Berkoff West in Decadence and Other Plays (1985) 121: No frighteners.
1989		J. Morton Lowspeak.
2004		N. ‘Razor’ Smith A Few Kind Words and a Loaded Gun 3: I was always the gunman, the ‘heavy’, the ‘frightener’.

In phrases

get the frighteners (v.)

to become terrified.

1962		F. Norman Guntz 93: A load of geezers get the dead frighteners whenever a bird opens her north & south.
1969		F. Norman Norman’s London 23: That’s wen I start ter get the dead frighteners.

put the frighteners on (v.) (also put the frighteners in, put the frights on, stick the frighteners on)(UK Und.)

1. to menace, to blackmail, to threaten with violence.

1959		F. Norman Fings I i: Can’t frighten me, though. The Geezer ain’t been born that can put the frighteners on me.
1960		F. Norman in Daily Mail 18 May in Norman’s London (1969) 94: All you need is a team of tearaways who go around sticking the frighteners on the proprietors of the aforementioned gaffs.
1962		R. Cook Crust on its Uppers 28: They [...] couldn’t pay even when we put the frighteners in.
1968		D. Cammell Performance [film script] Putting the frighteners on flash little twerps.
1979		F. Norman Too Many Crooks Spoil the Caper 11: That didn’t put the frighteners on them at all.
1989		T. Blacker Fixx 85: Far from putting the frighteners on Luigi [...] he had been earnestly discussing pizza trays.
1991		R.G. Barratt ‘An Artful Dodger’ in What Do You Reckon (1997) [ebook] They used to put the frighteners on some bloke who worked at Corio whisky.
1998		P. Bailey Kitty and Virgil (1999) 245: They put the frighteners on him and he squealed.
2000		S. Maloney Big Ask 34: Bit rich [...] Sharpe and McGrath toting you along to put the frights on a government minister.
2004		N. ‘Razor’ Smith A Few Kind Words and a Loaded Gun 14: All we do is put the frighteners on them [...] Nobody gets killed.
2009		L. McIlvanney All the Colours 101: Somebody’d put the frigteners on him.
2012		I. Rankin Standing in Another Man’s Grave (2013) 85: You know he put the frighteners on her husband?
2023		A. Rawnsley in Observer 12 Nov. 🌐 Dr No [...] is ‘rumoured’ to have once put the frighteners on someone by nailing to a door the dead pet rabbit of his ex-girlfriend’s kid brother.

2. to terrify (with no criminal overtones).

1958		F. Norman in Vogue Oct. in Norman’s London (1969) 31: What would put the frighteners on them even more was the hysterical giggles of delight that came from the inside.
1991		D. Jarman letter 3 June Smiling in Slow Motion (2000) 13: Anthony Hopkins put the frighteners on the audience.
2000		Indep. Rev. 14 Aug. 7: That must have put the frighteners on Italian women.