Green’s Dictionary of Slang

1. the penis, esp. when erect.

[1779		Mimosa: or, The Sensitive Plant 7: She from the Colonel did receive / Breeding and French, and learnt to give / Poor Peregrine, a prong-head].
1836		‘Sally Duff’ in Frisky Vocalist 22: All day she did long / For a taste of the boys’ little magical prong.
c.1900		Confessions of Lady Beatrice 4: I felt the pronging of his prong. His hand cupped my nest.
1927		‘Ballad of Gaffer Hepelthwaite’ in Immortalia 2: That never yet a maiden did confront his aged e’en / Whose legs he did not yearn to part and place his prong between.
a.1940		‘Hairbreadth Harry in “The Rescue”’ [comic strip] in B. Adelman Tijuana Bibles (1997) 18: With one stroke I shall send my prong into your belly.
1945		‘Cats on the Rooftops’ in Mess Songs & Rhymes of RAAF 1939-45 1: You should hear his high crescendo when his mate is on the prong.
1948		(con. 1927) in Randolph & Legman Ozark Folksongs and Folklore (1992) II 618: P is for prick, the petrified prong.
1966		B. Jackson Get Your Ass in the Water (1974) 213: P is for prick, a pastified [petrified] prong, / they ranks from seven to twelve inches long.
1974		G.F. Newman You Flash Bastard 127: One hand clasped his scrotum while the other stroked the underside of his penis appraisingly. ‘This prong will look quite fetching on me.’.
1977		L. Bangs in Psychotic Reactions (1988) 235: I doubt if there are very many gigs where he doesn’t end up pogoing his pronger in some sweet honey’s hive.
1980		Maledicta IV:2 (Winter) 194: A pointed weapon may be involved, such as a pike, prong, pronger, harpoon.
1983		T. Paulin ‘As a White Lodge in a Garden of Cucumbers’ in Liberty Tree 17: Hilarious, his prong; / what a scream her fanny is.
1994		G. Indiana Rent Boy 8: He shifted [...] around to show off his partly stiff prong.
2002		A. Duff Jake’s Long Shadow 70: You need to get yourself [...] a nice white boy. Yo. With a big pronger you can hold onto while you’re givin’ it to ’im up the rear.

2. a finger.

1850

Morn. Chron. (London) 12 Apr. 6/3: [Crockford] generally had some thousands of Bank of England notes pinned to the table before hin by the dainty, flexible fingers [...] the fifties, twenties, and tens, under his three longer ‘prongs,’ and a sheet of ‘fivers’ under the guardiansshiip of his little finger.

3. a negative criticism.

1895

Mirror of Life 27 Apr. 10/3: These are facts, and should not be overlooked by the ‘knockers,’ who are never happy unless they are sending the ‘prong’ into the very soul of a man who is successful.

4. (drugs) a hypodermic syringe.

1935

A.J. Pollock Und. Speaks n.p.: Prong, a hypodermic needle.