neither fish nor fowl
Something or someone that does not belong to a definite group or known class; a strange person or thing; someone or something odd or hard to understand.
The man is neither fish nor fowl; he votes Democrat or Republican according to which will do him the most good.
Mrs. Harris bought a piece of furniture that was both a table and a chair. Mr. Harris said it was neither fish nor fowl.
The movie is neither fish nor fowl; it is a funny love story.
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Source: A Dictionary of American Idioms