Dock workers' organisation on the rise (3)
I believe the answer is:
cut
'dock' is the definition.
(thesaurus)
'workers' organisation on the rise' is the wordplay.
'workers' organisation' becomes 'TUC' (short for Trade Unions Congress).
'on the rise' says the letters should be written backwards.
'tuc' reversed gives 'CUT'.
(Other definitions for cut that I've seen before include "Excise" , "Reduce; joint (of meat)" , "Wound" , "Abbreviate" , "Gash" .)