Feathery scarf (3)
I believe the answer is:
'feathery scarf' is the definition.
(type of feathery garment)
This is the entire clue.
(Other definitions for boa that I've seen before include "Large constricting snake" , "Feathered neckwear - snake" , "Fluffy scarf of feathers" , "that's dangerous for South Americans" , "strangler" .)