# separatrix

> English word · Noun · IPA /sɛpəˈɹeɪtɹɪks/

## Definitions
1. The ⟨L⟩ or pipe ⟨|⟩ mark formerly used to divide integers from decimals.
2. Synonym of decimal point, which replaced such marks.
3. 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.
4. A terminator: a line on a partially-illuminated surface separating the lit and shaded regions.
5. The line between regions having different magnetic fields.
6. The boundary separating two modes of behavior in a differential equation.

## Etymology
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.

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/separatrix