Learned line to repeat (8)
I believe the answer is:
literate
'learned' is the definition.
(synonyms)
'line to repeat' is the wordplay.
'line' becomes 'l' (used when specifying particular lines from a poem).
'to repeat' becomes 'iterate' (synonyms).
'l'+'iterate'='LITERATE'
(Other definitions for literate that I've seen before include "Scholarly" , "version of 'speed of light'?" , "Well versed in books" , "Learned" , "Well-read" .)