the.com/adultery

means Sex with someone who isn't your spouse while you're married to someone else.

from From Latin adulterare, 'to corrupt or defile,' built from ad- (toward) plus alter (other) — literally a turning toward another. The English word has no real root connection to 'adult,' despite the visual tease; that's a coincidence of spelling, not shared history. Latin used the same root for adulterating wine or metal — cutting the pure thing with something foreign — and the moral sense, corrupting a marriage with 'another,' rode in on that same idea of contamination.