Giant object in brown (5)
I believe the answer is:
titan
'giant' is the definition.
('titan' can be a synonym of 'giant')
'object in brown' is the wordplay.
'object' becomes 'it' (pronoun for an inanimate object**).
'in' indicates putting letters inside.
'brown' becomes 'tan' (tan is a kind of brown).
'it' going inside 'tan' is 'TITAN'.
(Other definitions for titan that I've seen before include "Rhea, perhaps" , "Person of heroic stature" , "Person of great strength - moon of Saturn" , "Gigantic Greek god" , "Taint in a great man" .)