1540s, "action of failing;" 1550s, "action of deserting a party, leader, etc." from Latin defectionem (nominative defectio) "desertion, revolt, failure," noun of action from past participle stem of deficere (see deficient). Originally used often of faith.
1. He denounced the defection as a stab in the back.
2. His defection to the other side was the ultimate betrayal.
3. The successful defection of Lyalin presented MI 5 with a unique opportunity.
4. It was he who first fingered Philby in the USA after defection of Burgess and Maclean.
5. Houghton, Lonsdale, and presumably also the Krogers would all be blown by the defection.