What part of speech is border?

Answer 1

The noun 'border' is a singular common noun.

The noun 'border' is a concrete noun as a word for the edge of something or decoration along the edge of something.

The noun 'border' is an abstract noun as a word for a line separating two political or geographical areas.

Answer 2

"border" could be a noun: We crossed the border.

"border" could be a verb: That state borders on Texas.