grammatical roles - "To hunt is my favorite pastime." What part of speech is "to hunt" in this sentence?

The function of infinitives seems to be up for grabs at the last post I commented at. I either need to be schooled or my interlocutors do. May your answers bring some clarity.

These are your choices. There are eight: noun, pronoun, verb, adjective, adverb, preposition, conjunction, interjection.

Avoid answers like: subject, predicate, direct/indirect object, complement, etc. These are not parts of speech.

The last post:
What is the part of speech is "the door" in the sentence below?

Some definitions (premises):

1.A verbal is a verb form that functions as another part of speech, i.e., nouns or modifiers (adjectives or adverbs).

2.Infinitives are a subset of verbals.

Therefore,

3.Infinitives (yes, composed of two words) function as nouns, adjectives, or adverbs.

As far as I know, these are standard definitions and noncontroversial. I'm simply asking, based on these definitions what part of speech is "to hunt" functioning as in my sentence. I don't know if people are unaware of these definitions or I am seriously missing something, but no one seems to be able to pull the trigger and simply identify an infinitive in a sentence as either a noun, adjective, or adverb though this type of analysis is everywhere on the web and in the grammars on my desk. People seem to be stuck on saying these are verbs because of their form (which is understandable) but ignoring that they are verbals, which never function as verbs. Others forgo parts of speech altogether and jump to sentence analysis, i.e., subject/predicate/D.O./I.O./ complements and so forth.

I believe the fact that an English infinitive technically has two words is incidental and doesn't inhibit it from being analyzed a single part of speech (German, Latin, Spanish, French all have single word infinitives). Wouldn't it be odd that in all these languages, their infinitives could be analyzed as a part of speech because they are single words, but because English has an additional "infinitive marker" we can't? The fact that the "to" (when combined with an infinitive) is not identified as a part of speech should be the clue that it is uniquely bound to the infinitive and that both are functioning as a single word (and please don't say "to," in this case, is a preposition ).

So I'm ready to find better web sources and burn my grammars if someone who knows grammar better than me can resolve this. Thanks to those who have already commented.