sokuon

Sokuon, formally known as 促音, is a Japanese phonological unit represented in writing by a small kana っ in hiragana or ッ in katakana. It indicates a geminate or doubled consonant in the following syllable, a feature common to many Japanese words and loanwords.

Orthography and usage: In native Japanese words, the sokuon is written with a small tsu in kana sequences, such as かっこ (kakko) or きっぷ (kippu). In katakana, used for foreign or loanwords, the same function is shown with the small ツ, as in カップ (kappu). The small tsu never stands alone and appears in the middle of a word or word boundary to signal the doubling of the next consonant.

Pronunciation: The effect of the sokuon is the consonant in the following syllable being pronounced with greater length or a burst-like release. In romanization, this is shown as a doubled consonant, for example kakko, kippu, ippai, and がっこう (gakkō). The result is a pronounced stop or lengthened onset of the next consonant rather than an additional separate syllable.

Occasional and stylistic notes: The sokuon is a standard orthographic device and is not used before vowels in ordinary spelling. It also appears in stylized writing or dialogue to convey hesitation, stuttering, or emphasis. In historical and some dialectal forms, the pronunciation and use of consonant doubling can vary, but the modern kana system consistently marks it with っ or ッ.

Related concepts include the yōon (palatalized combinations formed with small ya/yu/yo) and general gemination of consonants in Japanese phonology.