(set theory) A mathematical operation that returns a set taking one or more sets as input.

(algebra) An operation taking one operand, such as the square, factorial or absolute value operation.

(algebra, computing) A symbol representing binary operation; an operator taking two operands.

(music) A form of Italian comic opera popular in the 18th century.

A letter addressed to one person, or more, but published (as for example in a newspaper) for the public to read.

(law) An application of a legal rule that automatically brings about a legal consequence.

Information that is widely known, but not acknowledged openly. / (dated) Information that is not widely known, despite being freely available.

Alternative spelling of postoperative

Alternative form of soap opera

Alternative spelling of cooperation