What is the meaning of crucial?

adjective

• Of extreme importance; vital to the resolution of a crisis.
  • usage: "a crucial moment in his career"; "a crucial election"; "a crucial issue for women"
  • synonyms: important
• Having crucial relevance.
  • usage: "crucial to the case"; "relevant testimony"
• Of the greatest importance.
  • usage: "the all-important subject of disarmament"; "crucial information"; "in chess cool nerves are of the essence"
  • synonyms: all-important, all important, essential, of the essence