Play a guitar casually (5)
I believe the answer is:
strum
'play a guitar casually' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for strum that I've seen before include "Sweep fingers over strings" , "Pluck the strings idly" , "Play idly on guitar etc" , "Plays guitar" , "Play badly on a guitar" .)