What part of speech is the italicized word in the sentence below? Four (score) and seven years ago, our forefathers brought forth upon this continent a new nation conceived in liberty and dedicated to the proposition that all men are created equal.

Normally the word score is a noun. it stands for the number twenty and can usually stand alone. However, when preceded by four, it takes on a different meaning. It cannot stand alone because fourscore now becomes an adjective. Fourscore modifies the word years. So, fourscore is part of the adjective phrase fourscore and seven.