Merriam-Webster Collegiate Dictionary - reduplication

 noun  Date: 1555  1. an act or instance of doubling or reiterating  2.  a. an often grammatically functional repetition of a radical element or a part of it occurring usually at the beginning of a word and often accompanied by change of the radical vowel  b.  (1) a word or form produced by ~  (2) the repeated element in such a word or form  3. anadiplosis  • reduplicative adjective  • reduplicatively adverb