Brown holds it, being a giant (5)
I believe the answer is:
titan
'a giant' is the definition.
('titan' can be a synonym of 'giant')
'brown holds it' is the wordplay.
'brown' becomes 'tan' (tan is a kind of brown).
'holds' means one lot of letters goes inside another.
'tan' going around 'it' is 'TITAN'.
'being' is the link.
(Other definitions for titan that I've seen before include "Giant of Greek mythology" , "heavyweight?" , "Atlas, possibly" , "one of great importance" , "Mythological giant" .)