reduplicative
adjective /ˌriːˈdjuːplɪkətɪv/
  /ˌriːˈduːplɪkeɪtɪv/
- (used about words) repeating a syllable or other part of the word, often with a slight change- Reduplicative expressions like ‘mishmash’ and ‘nitty-gritty’ illustrate the playful nature of English.