The word 'the' is a definite article, used before a noun to define the noun as a specific or a singular thing, or sometimes an adverb to modify an adjective or adverb in a comparative.
Examples:
As an article: She's the star of theshow.
As an adverb: I liked raspberry the best.
The part of speech for this particular word is a noun.
part of speech
The part of speech for "answer" is a noun.
adverb
what part of speech is beneath
The part of speech for "unfamiliar" is an adjective.
The part of speech of "came" is a verb.
The part of speech for "twirl" is a verb.
The part of speech for "explicit" is an adjective.
The part of speech for "indefinite" is an adjective.
The part of speech for "lecturer" is a noun.
The part of speech for "breezy" is an adjective.