Learned line to say again (8)
I believe the answer is:
literate
'learned' is the definition.
(synonyms)
'line to say again' is the wordplay.
'line' becomes 'l' (used when specifying particular lines from a poem).
'to say again' becomes 'iterate' (to iterate is say something again).
'l'+'iterate'='LITERATE'
(Other definitions for literate that I've seen before include "well expressed" , "version of 'speed of light'?" , "Well-read" , "Able to read and write" , "Relate it, being well read" .)