Stigma (Greek letter and numeral)

Stigma (Ϛ, ϛ) is a historic Greek ligature of sigma+tau that became a distinct symbol used also as the numeral for six; it appears in manuscripts, typography, and the Greek numeral system.

Stigma (Greek: stigma, written Ϛ uppercase and ϛ lowercase) is a historic mark in the written Greek tradition. Originally a ligature combining the letters sigma (σ) and tau (τ) used in medieval handwriting, the form later came to be used as a dedicated symbol for the number six in the Greek numeral system. The word stigma itself means "mark" or "puncture" in Greek, reflecting its origin as a written sign.

Form and function

Visually, stigma looks distinct from standard sigma forms; the lowercase ϛ often resembles a small s-like character with a tail, while the uppercase Ϛ is a more angular variant. In textual practice the ligature served as a shorthand for the consonant cluster /st/ and appeared frequently in Byzantine manuscripts and printed Greek until typefaces standardized separate letterforms.

Numeric use and historical development

As a numeral, stigma represents the value 6 in the Greek numbering tradition, where alphabetic characters stand for numbers. This numeric role has roots in the older alphabetic sequence that included the archaic letter digamma (ϝ), which originally represented the sound /w/ and occupied the sixth position. Over time the glyphs and functions of digamma and the sigma–tau ligature converged in appearance and use, so the stigma shape became the conventional sign for the numeral six.

Uses and distinctions

Manuscript abbreviation: scribes used the ligature to save space and speed writing when the sequence "+st+" occurred.
Numerals: in lists, dates, and inscriptions the stigma sign stands for 6 (for example, in numeral notation the characters for 1–9, 10–90, 100–900 use alphabetic symbols).
Typography and encoding: modern fonts and character sets include distinct glyphs for stigma so it can be rendered separately from sigma or digamma.

It is important not to confuse stigma with the ordinary letter sigma (σ or final ς) or with other archaic signs; though related historically, each mark has its own role in writing and numeration. For an overview of the broader alphabetic context see the Greek alphabet, and for the system that assigns letters numeric values see Greek numerals.