A gaggle of high-fliers (5)

I believe the answer is:

skein

I'm a little stuck... Click here to teach me more about this clue!

'a gaggle' is the definition.
(thesaurus)

I don't understand how the rest of the clue works.

(Other definitions for skein that I've seen before include "Coil of wool - flock of geese" , "Loosely coiled length of thread" , "Loosely coiled bundle of wool" , "Loose bundle of yarn" , "Flock of flying geese" .)

I've seen this clue in the Evening Standard.

Want a hint initially instead of a full solution? Install my app