(abbreviation, alt-of, countable, initialism, uncountable) Initialism of old boy (a male graduate; also a CB radio operator's term of address for a male).
One woman in ten is at risk — yet one-third of all women over 50 have never had a mammo! By making Pap tests routine, OBs and GYNs have saved many lives. 1989, Contemporary Obstetrics-gynecology, volume 33, page 200:
(abbreviation, alt-of, countable, uncountable) Abbreviation of obstetrics.