the.com/skein

means A skein is a loosely coiled length of yarn or thread, wound into a bundle for storage, or — by extension — any tangled, winding mass or group in flight (like a skein of geese).

from From Middle English 'skeine,' borrowed from Old French 'escaigne,' meaning a hank or coil of thread — its roots before that are murky, possibly tangled up (fittingly) with other old Romance words for winding and looping. The word kept its coiling sense intact for centuries, which is how it drifted to describe geese flying in loose, looping lines across the sky.