Operation  n. 1 action, scope, or method of working or operating. 2 active process. 3 piece of work, esp. One in a series (begin operations). 4 act of surgery on a patient. 5 military manoeuvre. 6 financial transaction. 7 state of functioning (in operation). 8 subjection of a number etc. To a process affecting its value or form, e.g. Multiplication. [latin: related to *operate]