polish vs smoothen

polish is a noun but smoothen is not a noun.

Word	Noun	Adjective	Verb	Adverb
polish	Yes	No	Yes	No
smoothen	No	No	Yes	No

As verbs, polish and smoothen are synonyms defined as:

Other synonyms of polish include shine, smooth.

polish (noun)	smoothen (noun)
the property of being smooth and shiny
a highly developed state of perfection; having a flawless or impeccable quality
a preparation used in polishing

polish (verb)	smoothen (verb)
bring to a highly developed, finished, or refined state	become smooth
improve or perfect by pruning or polishing	make smooth or smoother, as if by rubbing
make (a surface) shine	make (a surface) shine