Who's beautiful? A lecturer is! (6)
I believe the answer is:
adonis
'who's beautiful?' is the definition.
(mythical beautiful youth)
'a lecturer is' is the wordplay.
'lecturer' becomes 'don' (don can mean an academic).
'a'+'don'+'is'='ADONIS'
(Other definitions for adonis that I've seen before include "extremely handsome chap" , "Handsome fellow" , "ideal man" , "handsome lad" , "No aids (anag)" .)