The Collaborative International Dictionary
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.
Wiktionary
n. A person with blood type O, which lacks antigens, and is therefore compatible with all other blood types, allowing such person to donate blood to any other person.
WordNet
n. a person whose type O Rh-negative blood may be safely transfused into persons with other blood types
Usage examples of "universal donor".
Watching Molly come out of one small shop only to begin immediately window shopping at the next shop, reminded him of the intensity at which she had pursued her idea of producing a universal donor species.
That was how he knew she was a universal donor, that was why she'd left the bounce-box with him.
He was a universal donor, but he knew that all of the inoculations he'd had as he'd traveled around the world would make him ineligible.
He was a universal donor, but he knew that all of the inoculations he'd had as he'd travelled around the world would make him ineligible.
Human genes trimmed in some lab in Sol system to make it a universal donor.