An archangel could be real big (7)
I believe the answer is:
gabriel
'an archangel' is the definition.
(I've seen this before)
'could be real big' is the wordplay.
'could be' indicates anagramming the letters.
'real'+'big'='realbig'
'realbig' with letters rearranged gives 'GABRIEL'.
(Other definitions for gabriel that I've seen before include "Archangel who plays the trumpet" , "musician" , "Dante - Rossetti, nineteenth century English poet/painter" , "Angel of Annunciation" , "Chief guard of Paradise" .)