Two successive lines of verse (7)
I believe the answer is:
couplet
'two successive lines of verse' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for couplet that I've seen before include "Two successive lines of verse, usually rhyming" , "Pair of verse lines" , "piece of poetry" , "Two lines of verse, often rhyming" , "Pair of lines in poetry" .)