[1590–1600; un-2 + shell]This word is first recorded in the period 1590–1600. Other words that entered Englishat around the same time include: Byzantine, dummy, fixture, jolt, radiusun- is a prefix freely used in English to form verbs expressing a reversal of some actionor state, or removal, deprivation, release, etc. (unbend; uncork; unfasten; etc.), or to intensify the force of a verb already having such a meaning (unloose)