outsider; alien element
Refers to a person or thing that is different from the rest of a group, often implying they do not belong or are incompatible. Used in social, organizational, or scientific contexts.
He was treated as an outsider at his new workplace.
There is no room for alien elements to infiltrate this organization.
異物 refers to a foreign object or contaminant, often physical, whereas 異分子 can be used for people or abstract elements.
Compound of 異 (different) and 分子 (molecule, element), literally 'different molecule/element'. The term is used metaphorically to describe a person or thing that does not fit into a group.