American Heritage® Dictionary of the English Language, Fourth Edition
- n. Mathematics The symbol (+), as in 2 + 2 = 4, that is used to indicate addition or a positive quantity.
- n. Chemistry The same symbol, used to indicate dextrorotatory rotation of polarized light.
- n. arithmetic The symbol + used to denote the operation of addition and to indicate that a number is positive.
GNU Webster's 1913
- adj. (Math.) the sign (+) which denotes addition, or a positive quantity.
- n. a sign indicating the operation of addition
“Darlington used symbols a plus sign for normal wings, a minus sign for shrunken to designate wing morphology, but for our purposes it’s as easy to talk about full-winged and shrunken-winged species.”
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