1610s, "unity, arithmetical unit," 1610s, from Late Latin monas (genitive monadis), from Greek monas "unit," from monos "alone" (from PIE root *men- (4) "small, isolated"). In Leibnitz's philosophy, "an ultimate unit of being, a unit of the universal substance" (1748); he apparently adopted the word from Giordano Bruno's 16c. metaphysics, where it referred to a hypothetical primary indivisible substance at once material and spiritual. Related: Monadic; monadism.
