セックスsekkusu

1. noun, suru verb, intransitive verbsex; sexual intercourse
   今いまではセックスの話はなしをすることは顔かおを赤あからめることではなくなった。↗

   Now talking about sex is no blushing affair.
2. noun(one's) sex; gender

• Synonym性交せいこうWrittenWritten, medical-flavored term for sexual intercourse; close to the intercourse sense of 「セックス」 but never refers to biological sex or gender.
• Synonym性行為せいこういWrittenFormal term for a sexual act, common in legal and medical writing; 「セックス」 is the more everyday loanword.
• SynonymファックCasualVulgar loanword for sex, also used as an expletive; cruder than 「セックス」 and out of place in formal contexts.
• Related性別せいべつNeutralNeutral word for the male/female distinction; 「セックス」 can also mean gender, but this is the everyday choice, and it never means intercourse.
• Related寝るねるCasualBasically 'to sleep' or lie down; with a partner it can euphemistically hint at sex, where 「セックス」 says it outright.
• Related雌雄しゆうWrittenWritten word for male and female animals; also victory versus defeat or which side is stronger. Overlaps with 「セックス」 only in the gender sense, never intercourse.
• Related性せいNeutralCovers gender, desire and sexual activity, plus a 'nature' sense; frequent in compounds like 「性教育」. Broader in scope than 「セックス」.
• Related営みいとなみWrittenOriginally means activity or work, but also serves as a discreet written euphemism for sex; 「セックス」 is the direct way to say it.
• Related交尾こうびWrittenNormally refers to animal mating, as in 「交尾期」; applied to humans it sounds biological or belittling, so 「セックス」 is the usual word.
• Related交わるまじわるWrittenVerb meaning to associate or mingle, euphemistically to sleep with someone; written and understated, where 「セックス」 is blunt.
• Related交わりまじわりWrittenNoun for association or relations, also a written euphemism for intercourse; 「セックス」 is more direct about the act itself.
• Related抱くだくNeutralBasically 'to hold in one's arms' or embrace, but can euphemistically mean to sleep with someone; context decides, unlike direct 「セックス」.
• Related性愛せいあいWrittenWritten word for erotic love or desire rooted in sexual instinct; 「セックス」 stresses the act itself, so the two are not freely interchangeable.
• Related交合こうごうWrittenWritten, rather archaic word for intercourse or mating, usable of animals too; for everyday human sex 「セックス」 is the normal choice.
• Related交接こうせつWrittenWritten word covering intercourse and mating, but also contact and socializing; everyday talk of human sex uses 「セックス」.
• Related共寝ともねWrittenWritten, old-fashioned word for sharing a bed; it says only that people sleep together, not necessarily the intercourse 「セックス」 denotes.
• Related同衾どうきんWrittenLiterary word for sharing a bed, especially a man and a woman; unlike 「セックス」, it describes lying together and does not necessarily mean intercourse.
• Related房事ぼうじWrittenDiscreet written term for bedroom matters, typically a married couple's sex life; 「セックス」 is the everyday, direct word.
• Related情交じょうこうWrittenWritten word for intimacy or a sexual liaison; close to the intercourse sense of 「セックス」 but can stress the emotional bond instead.
• Related一発やるいっぱつやるCasualCrude slang built on 'doing it once' for having sex; more casual and vulgar than 「セックス」, unfit for formal contexts.
• RelatedおめこCasualVulgar Kansai term for the female genitals or for sex; cruder than 「セックス」, and it can also name the body part itself.

For everyday talk of sex, 「セックス」 is the default. In formal or written contexts use 「性交」 or 「性行為」; for a discreet euphemism, 「営み」 or 「房事」. Animal mating is 「交尾」, and gender is 「性別」. Words like 「共寝」「同衾」「寝る」「抱く」 only hint at sex through context. Crude slang includes 「ファック」「一発やる」「おめこ」. 「性」 covers gender and desire broadly, while 「性愛」 stresses erotic love rather than the act.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. 性交せいこう。交接こうせつ。
2. 男女だんじょ・雌雄しゆうの別べつ。性別せいべつ。