'Universal donor' definitions:

Definition of 'universal donor'

(from WordNet)
noun
A person whose type O Rh-negative blood may be safely transfused into persons with other blood types

Definition of 'Universal donor'

From: GCIDE
  • Universal donor \U`ni*ver"sal do"nor\, n. (Med.) a person belonging to the O blood group (of the ABO classification), who can safely donate blood to anyone. [PJC]