IPA: /ʌnˈnɛsəˌsɛri/
KK: /ʌnˈnɛsəˌsɛri/
Not needed or required; something that is not essential.
Bringing extra clothes on a short trip is often unnecessary.
Unnecessary → It is formed from "un-" (meaning not) and "necessary" (from Latin "necessarius", meaning required or essential). The word "unnecessary" means not required or not essential.
Think of 'not' ('un-') and something that is 'required' ('necessary') — this helps you remember that 'unnecessary' means something that is not needed.