Could is a modal auxiliary verb. It's usually used to express possibility in a conditional sentence. Example: You could come with me if you didn't have to work.
'would' is a verb and 'all' is an adjective.
All subjects are part of speech for they are all nouns.
it depends what word it is it could be any part of speech depending on the sentence
My Mommy could tell you the answer
Venom could be a noun.
An adverb of place.
The word binding could belong to more than one part of speech. It could be a participle or a noun.
It could either be an adjective or a pronoun. It depends in which context.
The word coming is a verb. It is the present participle of the verb come.
The word could've is a contraction. It is the contracted form of the words could and have.
"Say" is a verb.
The word come is a verb. Come is an irregular verb.