Commonly do (6)
I believe the answer is:
diddle
'do' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for diddle that I've seen before include "Slangily cheat or swindle" , "Fleece" , "Con - do - lidded (anag)" , "Did, and led out to cheat" , "Slang for cheat or swindle - nearly fiddle" .)