Meaning

noun a solution obtained by steeping or soaking a substance (usually in water)

noun the process of extracting certain active properties (as a drug from a plant) by steeping or soaking (usually in water)

noun (medicine) the passive introduction of a substance (a fluid or drug or electrolyte) into a vein or between tissues (as by gravitational force)

originFrom Middle English infusioun, from Old French infusion, from Latin infusio, infusionem (“a pouring into, a wetting, a dyeing, a flow”), from infundo.

Etymology from Wiktionary, CC BY-SA 3.0