Green’s Dictionary of Slang

1. anything that is exceptional in size, power etc.

1906		Marvel 17 Nov. 469: Well, it’s a licker!
1939		H.E. Bates My Uncle Silas 40: It’s a licker [...] Look at them bottles!

2. something that proves beyond one’s powers or comprehension.

1884		Leicester Chron. 28 June 12/5: How you manages to keep in clover with a tidy suit of togs and always a tanner to lend a poor brother [...] is a licker to me.
1895		W. Pett Ridge Minor Dialogues 77: It’s a licker to me where they git ’em all from.
1898		J.D. Brayshaw Slum Silhouettes 15: Ah! there now; that’s a licker. Nobody don’t know.
1915		‘Tod Sloan’ Tod Sloan by Himself 3: How to get up on the saddle was a licker to me.
1920		Marvel 12 June 5: It’s a fair licker to me how he gets into such marvellous form.
1980		Barltrop & Wolveridge Muvver Tongue 71: Women are a licker to me.