Green’s Dictionary of Slang

kennedy n.

[anecdotal: one Kennedy who was apparently killed with a poker]

1. a poker.

[UK]‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc.
[UK]‘Billy Bighead’ in Cove in Spedding & Watt (eds) Bawdy Songbooks (2011) IV 227: His cannister [was] crack’d with a kennedy.
[Aus]Bell’s Life in Sydney 23 Oct. 3/2: The man who ‘struck Buckley wid a Kinnidy’.
[UK]Athenaeum 29 Oct. 559: St. Giles’s perpetuates the memory of a... man... who was killed by a poker by calling that instrument a kennedy [F&H].
[UK]Hotten Sl. Dict.
[UK]Mirror of Life 11 May 6/2: Richardson brought ‘Kennedy’ (the poker) to bear [...] Down rolled the inspector; then the sergeant stepped into the breach, and he rolled over on to his superior; and then came the rank and file of the police force, only to be demolished in the same manner.
[UK]Binstead & Wells Pink ’Un and Pelican 208: ‘Kennedy’ Knight, the ‘Kennedy’ from his having once laid a man out with a poker after the fashion of the gent who first made the name famous by a similar exploit in St Giles’ many years ago.

2. a blow inflicted with a poker [f. a man who allegedly suffered thus in London’s St Giles slums].

[UK]W.E. Henley ‘Villon’s Good-Night’ in Farmer Musa Pedestris (1896) 175: Paste ’em, and larrup ’em, and lamm! / Give Kennedy, and make ’em crawl!

3. a cosh.

[UK](con. 1920s) J. White ‘Campbell Bunk’ in History Workshop 26: A rich vein of slang which harked back to an older London street culture [...] Words which were not current in ordinary working-class speech [...] kennedy (cosh) .

4. the penis [fig. use of sense 1].

[US]Maledicta IV:2 (Winter) 191: Thus the […] the kennedy (= poker) pokes the fires of Hell, the wedge enters the crack and the placket-racket engages with the placket.

In phrases

give someone kennedy (v.)

to strike someone with a poker.

[UK]Partridge DSUE (8th edn) 239/2: ca. 1820–1900.