It's a noun. A full sentence needs only a subject (noun) and a verb, and you can say, "Compassion exists." Therefore, since "exist" is a verb, "compassion" is a noun. You can use that trick for lots of words, and conversely, if it doesn't fit in a two-word sentence like that then you know it isn't a noun or a verb.
Compassion is a noun.
The part of speech for this particular word is a noun.
The part of speech that the word my is used as is an adjective.
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 civilian is English grammar.
The part of speech for the word diplomacy 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.
What "part of speech" is the word "said?"