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"to separate or divide" (threads, strands, fibers), Old English -slæfan, from stem of -slifan "to separate, split, cleave," from Proto-Germanic *slifanan, perhaps related to the root of slip (v.). Cf. German Schleife "a loop, knot, noose." Related: Sleaved; sleaving. As a noun, "knotted, tangled silk or thread," 1590s, from the verb; this is the word in Shakespeare's rauel'd Sleeue of Care ("Macbeth").