Many of our men used by American (8)
I believe the answer is:
numerous
'many' is the definition.
('numerous' can be similar in meaning to 'many')
'our men used by american' is the wordplay.
'used' indicates an anagram.
'by' is a charade indicator (letters next to each other).
'american' becomes 'us'.
'our'+'men'='ourmen'
'ourmen' anagrammed gives 'numero'.
'numero'+'us'='NUMEROUS'
'of' acts as a link.
(Other definitions for numerous that I've seen before include "Consisting of a large but indefinite number" , "Umpteen" , "Ever so many" , "Great in quantity" , "Many, multifarious" .)