IPA: /ʌnˈkʌmənnəs/
KK: /ʌnˈkɒmənnəs/
The state or quality of not being common or usual; rarity.
The uncommonness of the species makes it a subject of interest for researchers.
Uncommonness → It is formed from "un-" (meaning not), "common" (from Old French *comun*, meaning shared by all or usual), and "-ness" (meaning the state or quality of). The word "uncommonness" refers to the state of being not common or rare.
Think of 'not' ('un-') being added to 'common' to describe something that is rare or not usual.