Nothing knocked back a lot of keen descendants (7)
I believe the answer is:
lineage
'descendants' is the definition.
(thesaurus)
'nothing knocked back a lot of keen' is the wordplay.
'nothing' becomes 'nil' (eg nil is zero in football).
'knocked back' says the letters should be written backwards.
'a lot of keen' becomes 'eage' (I can't justify this - if you can you should believe this answer much more).
'nil' written backwards gives 'lin'.
'lin'+'eage'='LINEAGE'
Can you help me to learn more?
(Other definitions for lineage that I've seen before include "Ancestral line as seen in eagle" , "Descent (from an ancestor)" , "Direct descent" , "Line of descendants of an ancestor" , "Old family members" .)