The plus sign is probably a squashed version of the Latin word et
Plus and minus feel as ancient as counting, yet they are fairly recent inventions. Medieval scribes wrote P and M instead, a German arithmetic book used the signs for surplus and shortfall in 1489, and the plus itself seems to be a shorthand for et, the Latin 'and', much like the ampersand.
Earlier cultures managed without them. Egyptian hieroglyphs showed addition as a pair of walking legs heading the same way as the text, with legs facing backwards for subtraction. Nicole Oresme's 14th-century manuscripts contain what may be one of the first plus signs, but in early 15th-century Europe the usual marks were P and M with a bar above, for the Italian piu and meno. Those barred letters first appeared in print in Luca Pacioli's Summa de arithmetica, published in Venice in 1494. The minus may descend from that bar over the M, or from a quick scribble of the letter itself.
Johannes Widmann's 1489 treatise named the signs minus and mer, an old form of the German for more, but applied them to excesses and deficits rather than sums. Henricus Grammateus used them in the modern way in a book of 1518, and in 1557 Robert Recorde, who also designed the equals sign, brought them to English readers in The Whetstone of Witte.
The humble dash has three separate jobs in mathematics: subtracting, flipping a value to its additive inverse, and marking a negative constant. Usually the difference does not matter, though some teachers, early graphing calculators and the language APL raise the minus for negatives to keep them apart. Precedence can trip people up. In standard notation, minus five squared is minus 25 because the power is applied first, yet Microsoft Excel lets the unary minus bind tighter and returns 25. American speakers born before 1950 tend to say minus five where younger ones say negative five, although temperatures still get the older phrasing.
Beyond arithmetic the signs multiply. A trailing plus means an open range, as in age limits, and streaming brands such as Disney and Paramount tack one on to hint at extras. Blood groups use them to show whether the Rh factor is present, grades rise and fall by them, and music writes an augmented chord with a plus. In C, a doubled plus increments a variable, which is where the name C++ comes from, and in computing a negative zero can exist even though mathematics has no such thing.
Source: Plus and minus signs
