needed, necessary

need, necessity

question, problem on homework etc. / a question; a matter (of time etc.) / a problem (something that needs to be dealt with); a trouble / an issue; a matter

the action of taking something apart in order to study it; analysis / (mathematics) analysis

analyze

strict, close

necessary evil

necessity (quality or state of being necessary, unavoidable, or absolutely requisite)

unnecessary

needlessness