With a bit of luck, head of Kew Society gets acquitted (5)
I believe the answer is:
walks
'gets acquitted' is the definition.
(as in walking free in court)
'with a bit of luck head of kew society' is the wordplay.
'with' becomes 'w' (abbreviation).
'bit of' suggests taking the first letters.
'head of' suggests taking the first letters.
The first letter of 'luck' is 'l'.
The first letters of 'kew society' is 'ks'.
'w'+'a'+'l'+'ks'='WALKS'
(Other definitions for walks that I've seen before include "Paces" , "Rambles" , "Perambulates" , "Goes on foot" , "Travels by foot" .)