separatrix

Learned borrowing from Latin sēparātrīx, the feminine form of separator (originally owing to an implied līnea (“line”)), from sēparāre (“to divide; to separate”) + -trix (forming female agents). By surface analysis, separate +‎ -trix. First developed as a decimal mark among the medieval Arab mathematicians, whence a shorter variant gave rise to the decimal comma employed by many European countries and their former colonies.

separatrix (plural separatrixes or separatrices)

(typography, historical) The ⟨L⟩ or pipe ⟨|⟩ mark formerly used to divide integers from decimals.
Synonyms: pipe, slash

Hypernyms: decimal mark < radix point < point, mark, character, separator

Coordinate terms: decimal point (precise sense), decimal comma
- 1660, Jonas Moore, Moor's Arithmetick, page 13:
  Therefore in writing of decimall parts let the separatrix be always used.
(typography, obsolete) Synonym of decimal point, which replaced such marks.
(typography) The proofreader's mark resembling a slash ⟨ / ⟩ or vertical bar ⟨ | ⟩ placed after a note in the margin to indicate that it should replace the item(s) struckthrough in the running text or to separate it from other margin notes.
A terminator: a line on a partially-illuminated surface separating the lit and shaded regions.
(physics) The line between regions having different magnetic fields.
(mathematics) The boundary separating two modes of behavior in a differential equation.

English