A noun of the abstract type.
"to water the earth" is a verbal phrase- more precisely an infinitive phrase. It could be expressed as "to irrigate"
Saline is an adjective and a noun. If I'm asked what i put on my contact lens, I say saline (adjective)solution. The noun is used less often. "Saline is a metallic salt".
the prefix for irrigate is
part of speech
The part of speech for this particular word is a noun.
The part of speech for "answer" is a noun.
adverb
what part of speech is beneath
I had to irrigate the fields today.
The verb of irrigation is irrigate. As in "to irrigate something".
The part of speech for "explicit" is an adjective.
The part of speech for "twirl" is a verb.