Attend summit initially to intimidate (8)
I believe the answer is:
browbeat
'intimidate' is the definition.
(I've seen this before)
'attend summit initially' is the wordplay.
'attend' becomes 'beat' (I've seen this in other clues).
'summit' becomes 'brow' (brow is a kind of summit).
'initially' means one lot of letters go next to another.
'beat' put after 'brow' is 'BROWBEAT'.
'to' acts as a link.
(Other definitions for browbeat that I've seen before include "Intimidate, bulldoze" , "Threaten - bully" , "cow" , "Hector" , "Bully verbally" .)