posterior vs ulterior

posterior is a noun but ulterior is not a noun.

Word	Noun	Adjective	Verb	Adverb
posterior	Yes	Yes	No	No
ulterior	No	Yes	No	No

As adjectives, posterior and ulterior are synonyms defined as:

Other synonyms of posterior include later.

posterior (noun)	ulterior (noun)
the fleshy part of the human body that you sit on
a tooth situated at the back of the mouth

posterior (adjective)	ulterior (adjective)
located at or near or behind a part or near the end of a structure	lying beyond what is openly revealed or avowed (especially being kept in the background or deliberately concealed)
coming at a subsequent time or stage	beyond or outside an area of immediate interest; remote
	coming at a subsequent time or stage