Perfect concept by a learner (5)
I believe the answer is:
ideal
'perfect' is the definition.
(similar in meaning)
'concept by a learner' is the wordplay.
'concept' becomes 'idea' (I've seen this before).
'by' means one lot of letters go next to another.
'a learner' becomes 'l' (as in a learner driver with L-plates on their car).
'idea'+'l'='IDEAL'
(Other definitions for ideal that I've seen before include "Most suitable" , "Perfect; a standard of perfection" , "just the job" , "Just the ticket" , "Coal-mining waste" .)