Flying eagle in descent (7)
I believe the answer is:
lineage
'descent' is the definition.
(I know that descent can be written as lineage)
'flying eagle in' is the wordplay.
'flying' indicates an anagram (letters fly around into new positions).
'eagle'+'in'='eaglein'
'eaglein' with letters rearranged gives 'LINEAGE'.
(Other definitions for lineage that I've seen before include "Pedigree, family tree" , "Ancestry, sequence of descendants" , "Stock" , "Line of descent or ancestry" , "Family descent" .)