Judge an American god (5)
I believe the answer is:
janus
'god' is the definition.
(Roman god)
'judge an american' is the wordplay.
'judge' becomes 'j'.
'american' becomes 'us'.
'j'+'an'+'us'='JANUS'
(Other definitions for janus that I've seen before include "Roman god of doors and beginnings" , "Roman god of doors, usually two-faced - a month is named for him" , "Two-faced person" , "Two-faced god of gates and doors - Guardian cryptic crossword setter" , "Two-faced deity" .)