Deer confused about one duck (5)
I believe the answer is:
eider
'duck' is the definition.
(eider is a kind of duck)
'deer confused about one' is the wordplay.
'confused' is an anagram indicator.
'about' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'deer' anagrammed gives 'eder'.
'eder' placed around 'i' is 'EIDER'.
(Other definitions for eider that I've seen before include "Sea bird" , "Sea duck with soft down" , "ie Red (anag.)" , "Type of duck" , "Duck supplying down" .)