Release attention-seeker in relative, shortly (6)
I believe the answer is:
uncoil
'release' is the definition.
'attention-seeker in relative shortly' is the wordplay.
'attention seeker' becomes 'oi' (exclamation used to attract attention).
'in' is an insertion indicator.
'relative' becomes 'uncle' (uncle is a kind of relative).
'shortly' means to remove the last letter.
'uncle' with its last letter removed is 'uncl'.
'oi' put inside 'uncl' is 'UNCOIL'.
(Other definitions for uncoil that I've seen before include "Become unwound" , "Straighten out like snake" , "Straighten out, unwind" , "Straighten from a curled state" , "Straighten from a curled position" .)