mid-15c., earlier onlesse, from (not) on lesse (than) "(not) on a less compelling condition (than);" see less. The first syllable originally was on, but the quality of negation in the word and the lack of stress changed it to un-. "Except could once be used as a synonym for unless, but the words have now drawn entirely apart" [Century Dictionary].
early 15c. as a shortening of unless. Extended contraction lessen, less'n, U.S. dialectal, is attested from 1881.
"small harpsichord," 1520s, evidently from virgin, but the connection is unclear, unless it means "an instrument played by girls."
Latin, "unless," occurring in legal and administrative phrases used in English, from ni "not " + si "if."
late 14c., hampren "surround, imprison, confine; pack in a container; impede in motion or progress," of uncertain origin; probably from hamper (n.1), unless it is somehow connected to Middle English hamelian "to maim." Related: Hampered; hampering.
mid-15c., stote, "the ermine, especially in its brown summer coat," of uncertain origin. The word bears resemblance to Old Norse stutr "bull," Swedish stut "bull," Danish stud "ox," but the sense is difficult unless a common notion is "male animal."