IPA: /ɪˈnæptnəs/
KK: /ɪˈnæptnəs/
The quality of being unsuitable or not appropriate for a particular situation; a lack of skill or ability that leads to awkwardness or failure.
His inaptness in handling the project led to several mistakes.
Inaptness → It is formed from "in-" (meaning not) and "apt" (from Latin "aptus", meaning suitable or fit) combined with the suffix "-ness" (meaning the state or quality of). The word "inaptness" refers to the state of being not suitable or unfit.
Think of 'not' ('in-') being added to 'suitable' ('apt') to remember that 'inaptness' means the quality of being unsuitable.