About to get round deer (3)
I believe the answer is:
roe
'deer' is the definition.
(roe deer is a kind of deer)
'about to get round' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'to get' means one lot of letters goes inside another.
'round' becomes 'o' (o is a circular letter).
're' going around 'o' is 'ROE'.
(Other definitions for roe that I've seen before include "Fish eggs; small deer" , "A mass of fish-eggs" , "Lobster's ripe ovary" , "Mass of fish's eggs" , "Food from fish" .)