1. To happen or take place.
    The liftoff will occur in exactly twelve seconds.
  2. To present or offer itself.
    I will write if the opportunity occurs.
  3. To come or be presented to the mind; to suggest itself.
  4. To be present or found.
    The chemical monofluoroacetate occurs in all parts of Dichapetalum cymosum, and is responsible for its toxic effects.

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