Deer confused about one duck (5)
I believe the answer is:
eider
'duck' is the definition.
(eider is a type 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' with letters rearranged gives 'eder'.
'eder' going 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" .)