somebody who donates blood, organs, etc for use in the medical treatment of others
a blood donor
a person who gives, donates, or presents something, esp to a public or charitable cause
in chemistry, an atom that combines with another and provides the two electrons that are shared to make the bond
in physics, an impurity that is added to a semiconductor to increase the number of mobile electrons
[early French doneur from Latin donator, from donare to give]