IPA: //ʌnˈsuːtəblɪ//
KK: /ʌnˈsutəbli/
In a way that is not appropriate or fitting for a particular situation.
He dressed unsuitably for the formal event, wearing jeans instead of a suit.
Unsuitably → It is formed from "un-" (meaning not) and "suitable" (from Latin "suitabilis", meaning fitting or appropriate) and the suffix "-ly" (meaning in a manner). The word "unsuitably" means in a manner that is not fitting or appropriate.
Think of 'not' ('un-') being added to 'suitable' to remember that 'unsuitably' means something is done in a way that is not appropriate.