Set timer for joint (5)
I believe the answer is:
mitre
'for joint' is the definition.
(mitre joint is a kind of joint)
'set timer' is the wordplay.
'set' is an anagram indicator (instruction to set the letters).
'timer' with letters rearranged gives 'MITRE'.
(Other definitions for mitre that I've seen before include "Liturgical headdress" , "Item of headgear" , "Bishop's tall headdress" , "in which one might find a bishop" , "Bevelled joint that forms a corner" .)