William allowed back on first light (4)
I believe the answer is:
tell
'william' is the definition.
(I've seen this before)
'allowed back on first light' is the wordplay.
'allowed' becomes 'let' (to let is to allow or permit).
'back' says the letters should be written backwards.
'on' says to put letters next to each other.
'first light' becomes 'l' (1st letter of 'light').
'let' back-to-front is 'tel'.
'tel'+'l'='TELL'
(Other definitions for tell that I've seen before include "Grass - Swiss hero" , "Order" , "Count - give an account" , "William .... was legendary Swiss hero-archer" , "One who refused to accept tyranny" .)