tiptop vs A-one

tiptop is a noun but A-one is not a noun.

Word	Noun	Adjective	Verb	Adverb
tiptop	Yes	Yes	No	No
A-one	No	Yes	No	No

As adjectives, tiptop and A-one are synonyms defined as:

Other synonyms of tiptop include ace, crack, first-rate, super, top-notch, topnotch, tops.

tiptop (noun)	A-one (noun)
the extreme top or summit
the highest level or degree attainable; the highest stage of development

tiptop (adjective)	A-one (adjective)
of the highest quality	of the highest quality