1rare The action or an act of pouring a liquid on to something or someone.
2historical The pouring of water on the body or a part of the body for therapeutic purposes; an instance of this. Frequently with distinguishing word specifying the temperature of the water, especially in "cold affusion". Also figurative.
The administration of baptism by pouring or sprinkling water over a person's head (opposed to immersion and aspersion); an instance of this.
Early 17th century (in an earlier sense). From (i) French affusion parenchyma;.