÷ An obelus (pl. "obeli") is a symbol consisting of a line with dots above and below, , used to represent the mathematical division operation. This symbol is also known as a division sign. The word "obelus" comes from the Greek word for a sharpened stick, spit, or pointed pillar. This is the same root as that of the word "obelisk". Originally this sign (or a plain line) was used in ancient manuscripts to mark passages which were suspected of being corrupted or spurious.
The obelus was first used as a symbol for division in 1659 in the algebra book Teutsche Algebra by Johann Rahn. Some think that John Pell, who edited the book, may have been responsible for this use of the symbol. The obelus had been used by some writers to represent subtraction, and that usage continued in some parts of Europe (including Norway and, until fairly recently, Denmark). The symbol had also been used occasionally in Polish language typography to represent ranges (such as 6–9), although this usage is mostly discontinued.
Today the obelus remains in occasional use, primarily as a standalone symbol for the division operation itself (as on a calculator), or as an operator in elementary arithmetic. In most contexts division is now signified in other ways, usually by writing the operands one above the other separated by a line, or on the same line with the slash (or solidus) as the symbol signifying division. In many non-Anglophone countries the colon is used as a division sign: “a divided by b” is written as a : b.
