Geek in dinner date (4)
I believe the answer is:
nerd
'geek' is the definition.
(I've seen this before)
'in dinner date' is the wordplay.
'in' says the answer is hidden in the clue.
'NERD' is hidden in the letters of 'dinner date'.
(Other definitions for nerd that I've seen before include "one that's overly cerebral" , "knowledgable geek" , "Flag on poles; wide (headline)" , "Irritating person (slang)" , "Boringly studious person" .)