Unattractive learner in agony (5)
I believe the answer is:
plain
'unattractive' is the definition.
(similar in meaning)
'learner in agony' is the wordplay.
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'in' means one lot of letters goes inside another.
'agony' becomes 'pain' (I've seen this in another clue).
'l' put inside 'pain' is 'PLAIN'.
(Other definitions for plain that I've seen before include "Unembellished" , "Simple, ordinary" , "Simple, unadorned" , "Uncomplicated" , "Evident; not fancy" .)