Necessary

Words that a speaker uses to indicate that he thinks something must happen.

• What words indicate that something is necessary?
  must need to have to have got to
• What words describe something that is necessary?
  necessary compulsory essential imperative indispensable inevitable mandatory obligatory required unavoidable urgent vital
• What words refer to something that is necessary?
  necessity need obligation prerequisite requirement
• What words describe something that is not necessary?
  unnecessary extraneous incidental inessential needless nonessential uncalled-for unessential unnecessary unneeded