Learn lines to speak (8)
I believe the answer is:
converse
'speak' is the definition.
(conversing is a kind of speaking)
'learn lines' is the wordplay.
'learn' becomes 'con' ('con' can be a synonym of 'learn').
'lines' becomes 'verse' (I've seen this before**).
'con'+'verse'='CONVERSE'
'to' acts as a link.
(Other definitions for converse that I've seen before include "Turned round" , "speak" , "Exchange views" , "express thoughts and ideas?" , "discuss" .)