Look around initially observing very large duck (9)
I believe the answer is:
goosander
'duck' is the definition.
(I know that goosander is a type of fish duck)
'look around initially observing very large' is the wordplay.
'look' becomes 'gander' (informal term for a look or glance).
'around' means one lot of letters goes inside another.
'initially' says to take the initial letters.
'very large' becomes 'os' (abbreviation for oversize).
The initial letter of 'observing' is 'o'.
'o'+'os'='oos'
'gander' going around 'oos' is 'GOOSANDER'.
(Other definitions for goosander that I've seen before include "Waterbird" , "duck" , "Bird" .)