Length of flight (5)
I believe the answer is:
skein
This clue might be a double definition.
'length' is the first definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'flight' is the second definition.
(thesaurus)
'of' acts as a link.
Can you help me to learn more?
(Other definitions for skein that I've seen before include "A number of birds" , "Flock of flying geese" , "Piece of loose-coiled yarn" , "Coil of wool - flock of geese" , "Loosely-coiled bundle of wool" .)