auction vs auction off

auction is a noun but auction off is not a noun.

Word	Noun	Adjective	Verb	Adverb
auction	Yes	No	Yes	No
auction off	No	No	Yes	No

As verbs, auction and auction off are synonyms defined as:

Other synonyms of auction include auctioneer.

auction (noun)	auction off (noun)
the public sale of something to the highest bidder
a variety of bridge in which tricks made in excess of the contract are scored toward game; now generally superseded by contract bridge

auction (verb)	auction off (verb)
sell at an auction	sell at an auction