sex

Sex entered English in the late fourteenth century from Old French sexe, which descended from Latin sexus, the state of being male or female.‍​‌​‍​‌​‌​‍​‌​‌​‌​‍​‌​‌​‌​‍​‍​‍​‌​‌​‍​‌​‌​‌​‌​‍​‌​‌​‌​‍​‌​‍​‌​‍ The Latin word is most plausibly derived from secare, to cut or divide, making sexus literally a cutting — the division of humankind into two categories. The same root supplied a remarkably productive family of English words, all involving some form of cutting or separating: section, segment, dissect, bisect, intersect, insect (an animal cut into segments), and sect (a group cut off from a larger body). Even segment and sickle share it. The thread running through all of them is the image of a clean dividing line, and sexus names the oldest line human languages were called on to name.

For most of its history in English, sex meant only the category — male or female, a classification applied first to humans, later extended to animals, and from the eighteenth century onward to plants. Linnaeus's Systema Naturae (1735) and Species Plantarum (1753) formalised the botanical use, putting the sex of plants at the heart of his scheme of classification and startling contemporaries who had not thought plants had any. Writers distinguished the sexes, spoke of the fair sex or the gentle sex, and used the word with the same neutral, taxonomic weight as age, height, or station. The earliest English attestations are in Wycliffe's Bible (c. 1382) in Genesis 6:19, "of al thingis hauynge sowle of ony flesh, two thou shalt brynge in to the ark, that male sex and female lyuen with thee." Chaucer uses it in The Parson's Tale. Shakespeare uses it routinely for the category ("all of her sex," "the weaker sex"). Samuel Johnson's Dictionary (1755) defines it only as "the property by which any animal is male or female" — with no hint of what the word would come to mean two centuries later.

The modern sense of sexual activity is a late arrival. Isolated examples appear in the nineteenth century — the OED cites H. G. Wells using "sex" for the act in 1929, but earlier traces survive in medical and social writing — and the usage only became widespread in the 1920s, popularised in the cultural wake of Freudian psychology, the 1918 English translation of Freud's Drei Abhandlungen zur Sexualtheorie (Three Essays on the Theory of Sexuality, originally 1905), and a newly freer public discourse about the body. Marie Stopes's Married Love (1918), Alfred Kinsey's studies in the 1940s, and the general loosening of newspaper euphemism pushed the new sense to the front of the dictionary entry. By the 1960s, "to have sex" was the ordinary phrase; by the 1980s, most speakers no longer felt the older categorical sense as primary. An older meaning rarely disappears cleanly; it just gets quietly outvoted.

A persistent source of confusion is the identical Latin word sex meaning six, the source of sextet, sextant, sextuple, and sextile. The two are unrelated. The numeral descends from Proto-Indo-European *sweḱs, the common root that also produced Greek héx, Sanskrit ṣaṭ, Old Irish sé, Old English siex (modern six), and Lithuanian šeši. Sexus traces back instead to the verb secare and ultimately to PIE *sek- ("to cut"), which also gives scythe, saw, sedge, and segment. Their identical spelling in modern English is an accident of Latin sound change, not shared ancestry — a pair of homographs with nothing in common.

An alternative proposal connects sexus not to secare but to sequor ("to follow"), framing it as the quality one follows or belongs to by nature. The idea goes back to seventeenth-century antiquarians and was still being entertained in the early twentieth century, but the secare derivation is the majority view in modern Latin philology. De Vaan's Etymological Dictionary of Latin (2008) marks the question as unresolved but favours secare; Ernout and Meillet reach the same verdict with more reserve. Either way, the thought behind the word is clear enough: to sex something is to sort it.

Cognates across the Romance languages preserve the original meaning unchanged. French sexe, Italian sesso, Spanish sexo, Portuguese sexo, Catalan sexe, Romanian sex all mean both the biological category and, in modern usage, the act — the same semantic drift has happened across the family. German Geschlecht is unrelated (it goes back to Proto-Germanic *slahtiz, "lineage, kind"), but German has also borrowed Sex directly from English for the modern act-sense. Sexology, sexism, sexy, sex appeal, unisex, transsexual, and intersex are all twentieth-century coinages, each built on a root that for most of its two-thousand-year life had meant only a quiet act of classification.

The word has therefore travelled a curious arc. It begins as a Latin abstract noun for a division; it passes into French and English as a taxonomic term; it is used for five hundred years in a register so neutral that it appears on the first page of Genesis; and then, in the space of two generations, it is completely overwritten by a new sense taken from the consulting room. The older meaning survives in scientific writing and on census forms — sex at birth, sex-linked, sex ratio — but in ordinary English the word has been almost entirely repurposed. The cut that Latin named has been recut by modern usage.