IPA: //ʌnˈsuːtəbl//
KK: /ʌnˈsuːtəbl/
Not appropriate or fitting for a particular purpose or situation.
The dress was unsuitable for the formal event.
Unsuitable → It is formed from "un-" (meaning not) and "suitable" (from Latin "suitabilis", meaning fitting or appropriate). The word "unsuitable" means not fitting or not appropriate for a particular purpose or situation.
Think of 'not' ('un-') being added to 'fitting' ('suitable') — this helps you remember that 'unsuitable' means something that is not appropriate.