side effect

About 1.64 uses per million words.

Meaning

noun An unintended consequence, or secondary result, of any action, in addition to the main or intended consequence of that action.
The Eiffel programming language is somewhat purist in insisting that functions have no side effects.
noun An unintended consequence of a drug or therapy; usually an adverse effect, and not a beneficial one.
noun A change a in state outside of the local environment of the function being called.
The Eiffel programming language is somewhat purist in insisting that functions have no side effects.