Guy beginning to tickle family member (5)
I believe the answer is:
taunt
'guy' is the definition.
(both can mean to tease)
'beginning to tickle family member' is the wordplay.
'beginning to' suggests taking the first letters.
'family member' becomes 'aunt' (sister of a parent).
The initial letter of 'tickle' is 't'.
't'+'aunt'='TAUNT'
(Other definitions for taunt that I've seen before include "Bait with insulting remarks" , "Guy" , "Tease hurtfully" , "element of teasing" , "Insult" .)