Mainstay is a noun.
Fruits and vegetables are the mainstay of a healthy diet. Diary products of a mainstay of Wisconsin's economy.
Oil is the mainstay of Saudi Arabia's economy.The sailor used the mainstay to secure the mainmast forward.
The word "mainstay" is a noun. An example of a sentence containing the word would be: Tourism is the mainstay of this small harbor town.
The part of speech for this particular word is a noun.
part of speech
The part of speech for "answer" is a noun.
what part of speech is beneath
adverb
The part of speech for "explicit" is an adjective.
The part of speech for "lecturer" is a noun.
The part of speech for "rapid" is an adjective.
The part of speech for "breezy" is an adjective.