Geminate

Definition
A geminate is a consonant that has contrastively longer duration than its singleton counterpart. This phenomenon is akin to long vowels, represented a [Vː]. However, geminates are frequently represented as a series of two identical consonants, rather than as a single, long consonant.

Gemination is a contrastive process in Arabic, Estonian, Finnish, Classical Hebrew, Hungarian, Italian, Japanese, Latin, Luganda, Norwegian, Russian and Swedish.

Examples
Gemination is not a phonological process typically present in English, but can be found in compound nouns.
 * [tt] in cattail (compare consonant length in "catfish")

In Japanese gemination is a distinctive phonological feature.


 * [shusshin] (origin, source) vs. [shushin] (master, husband)