Combining vertical line above

Type the base letter first, then this mark. It attaches to the preceding letter and displays above it; by itself, it has no system-specific reading.

Two Latin-letter ways of writing Taiwanese Hokkien—POJ (Pe̍h-ōe-jī) and Tâi-lô—put it after the vowel carrying the tone, where it marks tone 8. In to̍k, it follows o; tone 8 is one of those systems' categories for a syllable's tone.

Taiwan's Ministry of Education keeps this traditional tone-mark method in its Tâi-lô scheme, revised in 2024. Its dictionary lists citation tones—the tone of a syllable said alone—while tones can change when syllables join in speech, a pattern called tone sandhi. Pe̍h-ōe-jī grew from missionary work to make Taiwanese Hokkien readable in Latin letters, including Christian teaching and church news, in the late 19th century. Taiwan Church News began in 1885 and became the first major Pe̍h-ōe-jī publication.

Is this the Greek accent?

No; Greek tonos is written with the acute accent. A Unicode 2.1.8 release note corrected the old association: Greek tonos belongs to the acute mark ́, not this vertical line.

Unicode also records this mark in an older Marshallese orthography, an older spelling system. A Unicode proposal identifies the below-position vertical line ̩ as its counterpart; phonetic notation, a way to record speech sounds, uses that lower mark to show that a sound forms a syllable.