1815, from Fr., lit. "to know (how) to do," from savoir "to know" (from L. sapere; see sapient) + faire (from L. facere; see factitious). Instinctive knowledge of the right course of action in any circumstance. French also has savoir vivre "ability in good society; knowledge of customs in the world."
Ease and dexterity in social and practical affairs: “Peter is a friendly person, but he lacks the savoir faire required for a successful career in the foreign service.” From French, meaning “to know how to act.”