Top clue wasted two lines (7)
I believe the answer is:
couplet
'two lines' is the definition.
(I've seen this before)
'top clue wasted' is the wordplay.
'wasted' is an anagram indicator.
'top'+'clue'='topclue'
'topclue' anagrammed gives 'COUPLET'.
(Other definitions for couplet that I've seen before include "Two lines of verse, often rhyming" , "bit of poetry" , "piece of poetry" , "Two successive lines of verse, usually rhyming" , "Pair of lines in poetry" .)