Ends day oddly in whirl (4)
I believe the answer is:
eddy
'whirl' is the definition.
(synonyms)
'ends day oddly' is the wordplay.
'oddly' indicates alternate letters (letters in odd-numbered positions).
'ends'+'day'='endsday'
The alternate letters of 'endsday' are 'EDDY'.
'in' is the link.
(Other definitions for eddy that I've seen before include "move in circles" , "Mini-whirlpool" , "Whirlwind" , "Turner at sea" , "Man" .)