Used other than figuratively or idiomatically: see open, wide. / (idiomatic, intransitive) To open one's mouth wide, to gape

(programming) The operator ## in the C or C++ preprocessor, which permits separate tokens to be joined into a single token.

(now rare) Frank, unsecretive; not concealing one's feelings. / With the breast exposed; (of clothing) not covering the breast.

(transitive) To use a sudden, quick hand motion to open (something relatively small like a book, a lighter, etc.).

plural of opal glass

(euphemistic) To defecate.

(computing) an operator that is placed in between the operands like it is commonly used in arithmetical and logical formulae and statements.

(computing) An operator that sets the value stored in the storage location(s) denoted by a variable name.

(investment, finance) The amount by which the income of a company is less than its expenditure.

(mathematics) The interchange of suitable rows and/or columns of a matrix in order to place a particular element on the diagonal (prior to some other operation)