Descent taking long time on rope (7)
I believe the answer is:
lineage
'descent' is the definition.
('lineage' can be a synonym of 'descent')
'long time on rope' is the wordplay.
'long time' becomes 'age' ('age' can be a synonym of 'long time').
'on' means one lot of letters go next to another.
'rope' becomes 'line' (I've seen this in other clues**).
'age' put after 'line' is 'LINEAGE'.
'taking' acts as a link.
(Other definitions for lineage that I've seen before include "Ancestral line as seen in eagle" , "Ancestry, sequence of descendants" , "Direct descent" , "Stock" , "Descent from ancestors" .)