Is front an abstract noun

Answer 1

It can be, as in front door, front row. It can also be a noun, and more rarely a verb. It also appears to be an adverb when used in "face front."

Answer 2

The noun front can be a concrete or an abstract noun; for example, store front or a front end are things that can be seen and touched; a weather front or a business front are things that are concepts. There are even uses of 'front' for things that have no front or back (A ball has no front or back. Is this a concrete or abstract use of the word front?) and things that it's a matter of opinion which is the front (Do I have this on backwards?).

Answer 3

Yes, the noun 'frontier' is an abstract noun, a word for a concept.