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causa sine qua non

[kou-sah si-ne kwah nohn; English kaw-zuh sahy-nee kwey non, kaw-zuh sin-ey kwah nohn]
noun Latin.
  1. an indispensable condition; requisite.

Origin of causa sine qua non

literally, a cause without which not
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018