poor fish vs pudden-head

poor fish and pudden-head both are nouns.

Word	Noun	Adjective	Verb	Adverb
poor fish	Yes	No	No	No
pudden-head	Yes	No	No	No

As nouns, poor fish and pudden-head are synonyms defined as:

Other synonyms of poor fish include dolt, dullard, pillock, pudding head, stupe, stupid, stupid person.

poor fish (noun)	pudden-head (noun)
a person who is not very bright	a person who is not very bright