Green’s Dictionary of Slang

1. (UK Und.) a villain who steals a proportion of the gang’s joint booty.

1821		‘A Real Paddy’ Real Life in Ireland 185: Thus was Brian surrounded by rebels [...] swabbers, ticklers, weeders, sloemouths, and potato stalks.
1865		Leaves from Diary of Celebrated Burglar 32/1: I can plainly see ’tis a losing game to have such bloody ‘weeders’ along with me at ‘graft.’.

2. (US Und.) a thief.

1909

F.H. Tillotson How I Became a Detective 96: Weeder – One who carries the keys and unlocks stores and robs them systematically and locks the store again when leaving.

3. (US Und.) one who steals in small amounts to avoid detection.

1949		Monteleone Criminal Sl. (rev. edn) 250: weeder A person who steals in small amounts to avoid detection.
1976		M. Braly False Starts 124: Weeders took the smallest and most expensive items.