Definition of infidelity noun from the Oxford Advanced Learner's Dictionary

 

infidelity

 noun
noun
BrE BrE//ˌɪnfɪˈdeləti//
 
; NAmE NAmE//ˌɪnfɪˈdeləti//
 
[uncountable, countable](pl. infidelities)
 
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the act of not being faithful to your wife, husband or partner, by having sex with somebody else synonym unfaithfulness marital infidelity She could not forgive his infidelities. her infidelity to her husband His reputation has been damaged by allegations of marital infidelity. opposite fidelity Word Origin late Middle English (in the senses ‘lack of faith’ and ‘disloyalty’): from Old French infidelite or Latin infidelitas, from infidelis ‘not faithful’, from in- ‘not’ + fidelis ‘faithful’ (from fides ‘faith’, related to fidere ‘to trust’).
See the Oxford Advanced American Dictionary entry: infidelity