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Cyclopedia of Biblical, Theological and Ecclesiastical Literature [1]

( Χοῖνιξ , rendered "measure" in our version,  Revelation 6:6), a Greek measure of capacity, equal in dry commodities to one eighth the modius (See Bushel), but varying, according to different ancient authors, from one and a half to two pints English. (See Metrology).

International Standard Bible Encyclopedia [2]

kē´niks ( χοῖνιξ , choı́nix ): A G reek dry measure, almost equal to one quart. Mentioned in the New Testament only in  Revelation 6:6 , where the Revised Version, margin would read "choenix" instead of the indefinite translation "measure." The verse is then obviously a threat of famine.