IPA: //nɒnˈɛkstənt//
KK: /nɑnˈɛkstənt/
Not existing or no longer in existence.
The species was declared nonextant after years of habitat destruction.
Nonextant → It is formed from "non-" (meaning not) and "extant" (from Latin "extans", meaning standing out or existing). The word "nonextant" means not existing or not present.
Think of 'not' ('non-') and 'existing' ('extant') to remember that 'nonextant' refers to something that does not exist.