From Longman Dictionary of Contemporary Englishextramaritalex‧tra‧mar‧i‧tal /ˌekstrəˈmærətl◂/ adjective [only before noun] SYan extramarital sexual relationship is one that a married person has with a person who is not their husband or wife
Examples from the Corpus
extramarital• We were familiar with each breath, each movement, each thought, and his extramarital activities never diminished our mutual lust.• Though political partners, their personal relationship was shattered in 1918 when she discovered his extramarital affair.• The depositions touch on rumors of illegal drug use, extramarital affairs and petty squabbling.• Lawyers and presidents appear especially prone to getting trapped in extramarital affairs these days, at least in the view of Hollywood.• By the time we returned to the bar Karen's extramarital virginity had been lost beyond recall. unemployed. 