Line to appear conversational (4)
I believe the answer is:
seam
'line' is the definition.
(I know that line can be written as seam)
'appear conversational' is the wordplay.
'appear' becomes 'seem' (synonyms).
'conversational' indicates a 'sounds like' (homophone) clue (how it might sound in conversation).
'seem' sounds like 'SEAM'.
'to' acts as a link.
(Other definitions for seam that I've seen before include "Joint between two edges" , "Stitched joint" , "Stratum of ore or coal" , "Fabric join" , "A layer of coal in ground" .)