IPA: //ʌnˈraɪpər//
KK: /ʌnˈraɪpər/
This word describes something that is less ripe than another, meaning it has not yet reached full maturity or readiness.
The unriper fruit was still green and hard, unlike the ripe ones that were sweet and soft.
Unriper → It is formed from "un-" (meaning not) and "ripe" (from Old English "rīpe", meaning fully matured or ready to eat). The word "unriper" means not fully matured or less ripe than something else.
Think of something that is 'not' ('un-') 'fully matured' ('ripe') — that's why unriper refers to something that is less ripe.