Merriam-Webster Collegiate Dictionary - duplicate

 I. adjective  Etymology: Middle English, from Latin duplicatus, past participle of duplicare to double, from duplic-, duplex  Date: 15th century  1. consisting of or existing in two corresponding or identical parts or examples ~ invoices  2. being the same as another ~ copies  II. verb  (-cated; -cating)  Date: 15th century  transitive verb  1. to make double or twofold  2.  a. to make a copy of a cell ~s itself when it divides  b. to produce something equal to trying to ~ last year's success  c. to do over or again often needlessly ~d effort  intransitive verb to become ~d; also repeat  • duplicative adjective  III. noun  Date: 1532  1.  a. either of two things exactly alike and usually produced at the same time or by the same process  b. an additional copy of something (as a book or stamp) already in a collection  2. one that resembles or corresponds to another ; counterpart  3. two identical copies — used in the phrase in ~  Synonyms: see reproduction