International Standard Bible Encyclopedia
vān : The adjective of "vanity," and representing the same Hebrew and Greek words as does the latter, with a few additions (chiefly κενός , kenós , "empty," and its compounds in the New Testament). And "vain" can always be replaced by its synonym "empty," often with advantage in modern English ( Job 15:2; 1 Corinthians 15:14 , etc.). The exception is the phrase "in vain," and even there the interchange can be made if some (understood) noun such as "ways" be added. So "to take God's name in vain" (Exodus 20:7; Deuteronomy 5:11 ) means simply to take it for an "empty" ("not good") purpose.
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Orr, James, M.A., D.D. General Editor. Entry for 'Vain'. International Standard Bible Encyclopedia. https://www.studylight.org/encyclopedias/eng/isb/v/vain.html. 1915.