separatrices

Noun

separatrix (plural separatrixes or separatrices)

1. (historical) The ⟨L⟩ or pipe ⟨|⟩ mark formerly used to divide integers from decimals.
   • Therefore in writing of decimall parts let the separatrix be always used.1660, Jonas Moore, Moor's Arithmetick, page 13

   Synonyms:

   pipe, slash

2. (obsolete) Synonym of decimal point, which replaced such marks.

   Synonyms:

   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.