Yes, rot is a proper word.
The word rot is a verb (rot, rots, rotting, rotted):
Paper money will rot if you bury it in the ground without moisture protection.
The word rot is a noun (uncountable, mass noun):
The potatoes show some rot so we should throw them out.
Some compound nouns for the noun rot: root rot, dry rot, brown rot, black rot, boll rot, etc.
The noun 'rot' is sometimes used as slang for 'nonsense'.