Pain in the side (6)
I believe the answer is:
stitch
'pain in the side' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for stitch that I've seen before include "One in time can save nine, they say" , "Tack; pain in side" , "Sharp pain in side of body caused by exercise" , "It's painful" , "A sewer may produce such" .)