Idiotic Head of Accounts is retiring before watershed? (7)
I believe the answer is:
asinine
'idiotic' is the definition.
(both can mean foolish or silly)
'head of accounts is retiring before watershed?' is the wordplay.
'head of' suggests taking the first letters.
'retiring' is a reversal indicator.
'before' says to put letters next to each other.
'watershed?' becomes 'nine' (nine o'clock is the UK TV watershed).
The first letter of 'accounts' is 'a'.
'is' backwards is 'si'.
'a'+'si'+'nine'='ASININE'
(Other definitions for asinine that I've seen before include "Extremely stupid or foolish" , "Silly like a donkey" , "Idiotic" , "Stupid (as a donkey?)" , "Jenny's often like this" .)