Osculate comes from the Latin noun osculum, meaning "kiss" or "little mouth." It was included in a dictionary of "hard" words in 1656, but we have no evidence that anyone actually used it until the 19th century—except for scientists who used it differently to mean "to have contact with." Today, osculate is used in geometry for the action of a pair of curves or surfaces that touch so that they have a common tangent at the point of contact. When osculate is used to mean "kiss," the context is typically humorous.