Bear loses head in whirlpool (4)
I believe the answer is:
eddy
'whirlpool' is the definition.
(an eddy is a small whirlpool)
'bear loses head' is the wordplay.
'bear' becomes 'teddy' (teddy bear is a stuffed toy).
'loses head' means to remove the first letter.
'teddy' with its initial letter removed is 'EDDY'.
'in' is the link.
(Other definitions for eddy that I've seen before include "religious leader" , "Swirling current" , "Fellow" , "Rapid circular current" , "Spinning current" .)