Green’s Dictionary of Slang

1. anything small, esp. a small fish.

1885		B.E. Martin in Harper’s Mag. May 866/1: Them’s tiddlers, they is .
1890		Music Hall & Theatre Rev. 15 Feb. 7/1: [of shots of whisky] [P]arting with half-a-crown for various ‘tiddlers’.
1930		Biz (Fairfield, NSW) 17 Jan. 3/4: Our friend the tiddler-tickler seems to have put the ginger into all the fishing fraternity.
1945		(con. 1919) R. Westerby Mad in Pursuit 26: Noisy boys fishing for tiddlers in the pond.
1957		‘Nino Culotta’ They’re a Weird Mob (1958) 71: Saw a tiddler crack him a while ago.
1963		A. Baron Lowlife (2001) 152: Your dad can take you down to the River Lea [...] Catch tiddlers in a jar.
1974		‘P.B. Yuill’ Hazell Plays Solomon (1976) 17: Rag Trade Reggie [...] needed somebody to look after his collection of exotic tiddlers.
1983		J. Sullivan ‘Friday the 14th’ Only Fools and Horses [TV script] rodney: We said we might do a little bit of fishing. del: Yeah, that’s right [...] just a little bit – tiddlers.
2000		Indep. Rev. 5 Feb. 20: Unlike the Paris tiddler, the London Eye does not take off like a rocket.
2001		A. Sillitoe Birthday 26: When I was a kid [...] I went after tiddlers, scooped ’em up in a jam jar.

2. a penis, usu. that of a small boy.

1980		Maledicta IV:2 (Winter) 190: Tiddler means not only a little boy’s whistle but that which is used to tiddle with.
1998		P. McCabe Breakfast on Pluto 24: No mickies today! Off with you and say your prayers for no tiddler stands for girls like these!

3. (Aus.) £1 sterling.

1941		Baker Popular Dict. Aus. Sl.
1955		N. Pulliam I Travelled a Lonely Land (1957) 240/2: tiddler – a one-pound note.

4. a threepenny piece.

1959

I. & P. Opie Lore and Lang. of Schoolchildren (1977) 175: A threepenny piece is a ‘bit’ or ‘tiddler.’.