necessary
/ˈnɛsəˌseri/ /Brit ˈnɛsəsri/
adjective
[more ~; most ~] :so important that you must do it or have it :absolutely needed
always used before a noun formal :unable to be changed or avoided
necessary evil
noun
plural -saries
necessaries [plural] :things (such as food, a place to live, and clothing) that you must have :necessary things
the necessary Brit informal :whatever is needed for some purpose