Green’s Dictionary of Slang

dicker n.1

also dikker
[abbr. SE dictionary + -er sfx2 ]

a dictionary.

[UK]Kipling ‘Propagation of Knowledge’ in Complete Stalky & Co. (1987) 227: Johnson started to learn Dutch when he was seventy. ‘What the deuce for?’ Stalky asked. ‘For a change after his Dikker, I suppose,’ Howell suggested.