Fool Herald now and then (7)
I believe the answer is:
airhead
'fool' is the definition.
(I've seen this in another clue)
'iheraldi now and then' is the wordplay.
I cannot quite see how this works, but
'now' could be 'ad' (AD, Anno Domini, as opposed to BC, Before Christ) and 'ad' is found in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for airhead that I've seen before include "Idiot" , "clown" , "Simple-minded soul" , "military base behind enemy lines" , "clot" .)