I'm included in an American hostility (6)
I believe the answer is:
animus
'hostility' is the definition.
(I know that animus is a type of hostility)
'i'm included in an american' is the wordplay.
'included in' means one lot of letters goes inside another.
'american' becomes 'US' (abbreviation for United States).
'an'+'us'='anus'
'im' placed inside 'anus' is 'ANIMUS'.
(Other definitions for animus that I've seen before include "Malicious ill-will" , "Hostile spirit in speech or action" , "spirit of hostility" , "Hostile feeling" , "Motivating spirit" .)