noun
extramarital intercourse; adultery
A formal, clinical term for sexual relations outside marriage. Often used in legal, medical, or sociological contexts. In everyday speech, 不倫 (ふりん) or 浮気 (うわき) are more common.
婚外性交は、一部の国では法的に罰せられる。
Extramarital intercourse is legally punishable in some countries.
この調査は婚外性交の実態を明らかにした。
This survey revealed the actual state of extramarital intercourse.
Compound of 婚外 (こんがい, 'outside marriage') and 性交 (せいこう, 'sexual intercourse'). A modern, formal coinage.