Probably a noun
When you add the suffix -ous to the word "poison," it becomes an adjective - "poisonous."
The poisonous part of the butterfly is infact the legs
No there is not a poisonous part in a lobster.
part of speech
The part of speech for this particular word is a noun.
what part of speech is beneath
what part of speech is work
adverb
Skin secretions
In the sentence "watch out for that poisonous snake," the word "out" is being used as an adverb, modifying the verb "watch" to indicate that one should be cautious.
the part of speech sashay is a averb