Is dress a noun or not?

It most certainly is; the Word dress is a singular, common, concrete noun, a Word for a garment, a thing. The Word dress is also a verb (dress, dresses, dressing, dressed) and an adjective (dress, dressier, dressiest). Example uses:

Noun: The dress is new but the shoes are not.

Verb: He can dress himself.

Adjective: How great he looks in his dress uniform.