The word "density" is a noun. It refers to the degree of compactness of a substance.
The part of a longitudinal wave with the lowest density is the rarefaction. This is where the particles are spread out, creating a region of lower density compared to the rest of the wave.
"Wavelength" is a noun.
An adjective
"Sunshine" is a noun.
Dew is a noun.
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.