early 15c., "to pour in, introduce, soak," from Latin infusus, past participle of infundere "to pour into," from in- "in" (see in-(2)) + fundere "pour, spread" (see found, v.2). Figurative sense of "instill, inspire" first recorded 1520s (infusion in this sense dates from mid-15c.). Related: Infused; infusing.