IPA: /ɪnˈkɒmpɪtənsi/
KK: /ɪnˈkɑːmpɪtənsi/
The state of not having the skills or ability to do something effectively or properly.
His incompetency in managing the project led to many mistakes.
Incompetency → It is formed from "in-" (meaning not) and "competent" (from Latin "competens", meaning suitable or qualified) and the suffix "-cy" (meaning the state or condition of). The word "incompetency" refers to the state of being not suitable or not qualified for a task or role.
Think of 'not' ('in-') being combined with 'suitable' ('competent') to remember that 'incompetency' means the state of not being suitable or qualified.