singular vs unusual

singular is a noun but unusual is not a noun.

Word	Noun	Adjective	Verb	Adverb
singular	Yes	Yes	No	No
unusual	No	Yes	No	No

singular (noun)	unusual (noun)
the form of a word that is used to denote a singleton

singular (adjective)	unusual (adjective)
grammatical number category referring to a single item or unit	not usual or common or ordinary
composed of one member, set, or kind	being definitely out of the ordinary and unexpected; slightly odd or even a bit weird
unusual or striking	not commonly encountered
being a single and separate person or thing
the single one of its kind
beyond or deviating from the usual or expected