(1) A person from whom blood, tissue, or an organ is taken for transplantation. (2) A compound that will transfer an atom or a radical to an acceptor; e.g., methionine is a methyl donor; glutathione is a glutamyl donor. (3) An atom that readily yields electrons to an acceptor, e.g., nitrogen, which will donate both electrons to a shared pool in forming a coordinate bond. [L. dono, pp. donatus, to donate, to give]