Brother held by arm on kayak (4)
I believe the answer is:
monk
'brother' is the definition.
(I've seen this before)
'held by arm on kayak' is the wordplay.
'held by' says the answer is hidden in the clue.
'MONK' is hidden in the letters of 'arm on kayak'.
(Other definitions for monk that I've seen before include "Member of a religious community" , "Man in a religious order" , "Setter" , "One vowed" , "Thelonious - - (jazz)" .)