Semi-hardy hairpiece (3)
I believe the answer is:
rug
'hairpiece' is the definition.
(rug is a kind of hairpiece)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for rug that I've seen before include "Wig (informal)" , "Mat or knee-cover" , "A bug may be snug in it" , "Small carpet" , "Hairpiece" .)