Clear line in drawing (5)
I believe the answer is:
plain
'clear' is the definition.
(similar in meaning)
'line in drawing' is the wordplay.
'line' becomes 'l' (used when specifying particular lines from a poem).
'in' is an insertion indicator.
'drawing' becomes 'pain' (I can't explain this - if you can you should give a lot more credence to this answer).
'l' placed inside 'pain' is 'PLAIN'.
Can you help me to learn more?
(Other definitions for plain that I've seen before include "lacking special beauty" , "Simple, unadorned" , "Unadorned on flat area" , "Obvious - ordinary" , "Not complicated" .)