IPA: /ʌnˈnɛsəˌsɛrəli/
KK: /ʌnˈnɛsəˌsɛrɪli/
In a way that is not needed or required; more than what is necessary.
She spent unnecessarily long hours on the project, which could have been completed in half the time.
Unnecessarily → It is formed from "un-" (meaning not) and "necessary" (from Latin "necessarius", meaning required or essential) and the suffix "-ly" (meaning in a manner). The word "unnecessarily" means in a manner that is not required or essential.
Think of 'not' ('un-') and 'required' ('necessary') to remember that 'unnecessarily' means something done in a way that is not needed.