ne plus ul·tra /ˌneˌplʌsˈʌltrə, ˌni-/
  Ne plus ul·tra
  1. The uttermost point to which one can go or attain; hence, the summit of achievement; the highest point or degree; the acme.
  2.  A prohibition against proceeding further; an insuperable obstacle or limiting condition. [Obs. or R.]
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  ne plus ultra
       n : the state of being without a flaw or defect [syn: perfection,
            flawlessness] [ant: imperfection]