Is it ensure, insure, or assure?
1570s, "action of pouring liquid from one vessel to another," from Latin transfusionem (nominative transfusio), noun of action from transfusus (see transfuse). Sense of "transfering of blood from one individual to another" first recorded 1640s.
transfusion trans·fu·sion (trāns-fyōō'zhən)
The transfer of whole blood or blood products from one individual to another.
The intravascular injection of physiological saline solution.
The transfer of blood or a component of blood, such as red blood cells, plasma, or platelets, from one person to another to replace losses caused by injury, surgery, or disease. Donated blood products are tested for blood type and certain infectious diseases and stored in blood banks until they are used. The blood of the donor is shown to be histologically compatible, or crossmatched, with that of the recipient before transfusion. See more at Rh factor. See Note at blood type.