odd fish vs odd man out

odd fish and odd man out both are nouns.

Word	Noun	Adjective	Verb	Adverb
odd fish	Yes	No	No	No
odd man out	Yes	No	No	No

As nouns, odd fish and odd man out are synonyms defined as:

odd fish and odd man out: someone regarded as eccentric or crazy and standing out from a group

Other synonyms of odd fish include kook, odd fellow, queer bird, queer duck.

odd fish (noun)	odd man out (noun)
someone regarded as eccentric or crazy and standing out from a group	someone regarded as eccentric or crazy and standing out from a group