Look ~n there's an opening for an egghead! (4)
I believe the answer is:
gape
'look' is the definition.
(gape is a kind of look)
'there's an opening for an egghead' is the wordplay.
'there's an opening' becomes 'gap' (synonyms).
'for' says to put letters next to each other.
'an egghead' becomes 'e' (head letter of 'egg').
'gap'+'e'='GAPE'
'n' acts as a link.
(Other definitions for gape that I've seen before include "watch in wonder" , "Look in amazement or stupidity" , "Stare stupidly" , "Look amazed" , "Gawp" .)