geminate

(noun) a doubled or long consonant. Examples: "The `n' in `thinness' is a geminate."

(verb) form by reduplication. Synonyms: reduplicate. Examples: "The consonant reduplicates after a short vowel." "The morpheme can be reduplicated to emphasize the meaning of the word."

(verb) occur in pairs. Synonyms: pair.

(verb) arrange in pairs. Synonyms: pair. Examples: "Pair these numbers."

(verb) arrange or combine in pairs. Examples: "The consonants are geminated in these words."