Spendthrift was on line after time (7)
I believe the answer is:
wastrel
'spendthrift' is the definition.
(I've seen this in another clue)
'was on line after time' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'line' becomes 'l' (used when specifying particular lines from a poem).
'after' says to put letters next to each other.
'time' becomes 't' (abbreviation).
're'+'l'='rel'
'rel' after 't' is 'trel'.
'was'+'trel'='WASTREL'
(Other definitions for wastrel that I've seen before include "Good-for-nothing person" , "Worthless person" , "A useless, good for nothing fellow" , "Spendthrift" , "Profligate" .)