It is an adjective. It can be used as a noun, as in "He was in solitary", but the full version of that is "He was in solitary confinement". So the noun is being left out as the sentence is abbreviated, turning the adjective into a noun.
The word solitary is a noun and an adjective. The noun form is someone who lives alone. The adjective form means to be living alone.
The part of speech that the word my is used as is an adjective.
The part of speech for this particular word is a noun.
The part of speech for the word civilian is English grammar.
The part of speech for the word diplomacy is a noun.
H is a letter, not a word. To be a part of speech, it needs to be a word.
The part of speech for the word "boulevard" is a noun.
The word speech is a noun.
The part of speech for this particular word is a noun.
The word speech is a noun.
The word speech is a noun.
The word speech is a noun.