Forget about entrance to Oxford and Cambridge university (4)
I believe the answer is:
omit
'forget about' is the definition.
(I've seen this in another clue)
'entrance to oxford and cambridge university' is the wordplay.
'entrance to' suggests taking the first letters.
'and' says to put letters next to each other.
'cambridge university' becomes 'MIT' (MIT in Cambridge, Massachusetts).
The initial letter of 'oxford' is 'o'.
'o'+'mit'='OMIT'
(Other definitions for omit that I've seen before include "Leave something out" , "Leave out or overlook" , "Fail (to do something)" , "Leave out, do not include (4)" , "Don't include" .)