Clasp fifth letter containing a complaint (5)
I believe the answer is:
gripe
'a complaint' is the definition.
(an objection or source of annoyance)
'clasp fifth letter' is the wordplay.
'clasp' becomes 'grip' (synonyms).
'fifth letter' becomes 'e' (5th letter of 'letter').
'grip'+'e'='GRIPE'
'containing' is the link.
(Other definitions for gripe that I've seen before include "Complain; colic (water)" , "Grievance" , "carp" , "Complain; stomach pain" , "Complain, grouse" .)