(By Carl Rubino): "The repetition of phonological material within a word for semantic or grammatical purposes is known as reduplication, a widely used morphological device in a number of the world’s languages. The languages classified on the accompanying map are sorted into three categories: languages that do not employ reduplication as a grammatical device, languages that productively employ both partial and full reduplication, and languages that only employ full reduplication. ❡
Full reduplication is the repetition of an entire word, word stem (root with one or more affixes), or root. Examples are Nez Perce (Sahaptian; northwestern United States) full word lexical reduplication: té:mul ‘hail’ vs. temulté:mul ‘sleet’ (Aoki 1963: 43), or Tagalog full root reduplication, shown here with the verbalizing prefix mag-, where the reduplicant isip is identical to the base isip ‘think’: mag-isip ‘to think’ vs. mag-isip-isip ‘to think about seriously.’ ❡
Partial reduplication may come in a variety of forms, from simple consonant gemination or vowel lengthening to a nearly complete copy of a base. In Pangasinan (Austronesian; Philippines) various forms of reduplication are used to form plural nouns."