To reconstruct an ancient root with a measure of verisimilitude is not too hard. However, it should be borne in mind that the roots are not the seeds from which words sprout, for we compare such words as are possibly related and deduce, or abstract their common part. Later we call this part “root,” tend to put the etymological cart before the horse, and get the false impression that that common part generates or produces words. The plant metaphor in linguistics (word roots, stems, trees, language branches, and so forth) has in general little to recommend it despite its venerable age and the clear message of its inner form. (The German noun Stammbaum appears even in English dictionaries.)
So what is the “root” of the word breast? Among the words close to breast we find burst, from bersten, in which er owed its existence to metathesis (the transposition of e and r). As follows from the cognates elsewhere in Germanic, the verb’s protoform must have been brestan. The similarity between Old Engl. brēost and brestan is unmistakable, and nearly all the older dictionaries that feature this word connect breast with burst. The reservation (…that includes this word…) is not a tribute to pedantry. For example, Stephen Skinner (1671) and a later anonymous dictionary (Gazophylacium) skipped breast. Junius (1743, a posthumous edition) mentioned it but offered a fanciful etymology from Greek. The others, including Skeat (in the first edition of his great dictionary), stuck to burst.
But why should the breast burst? One could think of a human breast bursting with grief along the Byronic lines:
“But bid the strain be wild and deep,
Nor let thy notes of joy be first:
I tell thee, Minstrel, I must weep
Or else this heavy heart will burst;
For it hath been by sorrow nurst,
And ached in sleepless silence long;
And now ‘tis doomed to know the worst,
And break at once—or yield to song”
(“My Soul Is Dark,” from his Hebrew Melodies)
In principle, a poetic word, ancient or modern, for “breast” as the seat of passion is quite possible: compare the specification of Engl. bosom, (to a certain extent) Greek kólpos, and Latin sinus. It even seems that the speakers of Germanic did have such a word, namely Gothic barms (which rendered Greek kólpos), Old High German barm, and Old Engl. bearm. The context of bearm of course does not point to a bosom ready to burst. It means “bosom, lap, breast; middle, inside,” “possessions” (in poetry), and, less clearly, “emotion, excitement” (in a psalter). “Middle, inside” are especially telling senses. Whether native or borrowed, Old Norse barmr continues into the modern Scandinavian languages (barm) as a word sometimes belonging to the elevated style or endowed with unmistakable poetic connotations. It can also mean “a woman’s breast.” Not improbably, barm goes back to the same root as the verb bear “to carry” (from beran), that is, it denotes a place where either objects or feelings (!) could be hidden.
The German verb erbarmen “to move to pity” is known to have the root arm, not barm, for it glossed Latin miserere “to have pity” (arm means “poor”), so that the original form was er-b-armen. A similar process happened in Old English, but I cannot get rid of the suspicion that at least in Old High German the existence of barm contributed to the verb’s meaning “to move to pity.” If Gothic barms and its cognates sometimes referred to the breast as the seat of emotions, breast must have had a different meaning. Skeat (1882; actually 1879, because his etymological dictionary appeared in installments) wrote: “The original sense is a bursting forth, as applied to the female breast in particular.” We have already witnessed the attempt to explain bosom in the same terms. The female breast poses a great temptation even to grey-haired historical linguists. But as with bosom, there is no evidence that in old days breast referred to a woman’s body. Neither did barm, despite such an application of it in Modern Norwegian. Etymology, as I have noted more than once, makes great progress: as times goes on, it becomes more and more careful. In the last edition of his dictionary (1910), Skeat dismissed breast as a word of unknown origin. Some authorities followed his example.
Alongside burst (that is, brestan), verbs like Middle High German briezen “to bud, burgeon” (z = ss) have been proposed as supplying the clue to the origin of breast. The reference would be to the nipples on the breast, not necessarily of a woman. A similar conjecture also turned up in the works discussed in connection with bosom, which is not surprising: bosom and breast are close. Today most researchers share the idea that breast was named after its “buds.” In this light, the proto-Indo-European root had the form breu–s “to swell,” and again we find ourselves on familiar ground! It will be remembered that I tried to make a case for “swell” as the foundation of the word for bosom. No doubt, breast and bosom might have synonymous roots, mean more or less the same, and later acquire somewhat different meanings.
Facts, not opinions, matter in etymology, but what I am going to say is just that: an opinion. I believe that breast was not coined because a human breast has two nipples or two teats, though the ancient neuter dual might arise thanks to the clear division of the human breast into two sections. It probably emerged because it swells, rather than because of the sprouting “buds.” Last week I mentioned the fact that the word for “breast” was related to the Slavic name for “belly” (briukho). The not uncommon emphasis on what is inside the breast points away from the upper front surface of the body. If breast emerged as “a swelling, heaving organ,” only bosom perhaps referred specifically to the upper part of our anatomy, while breast was expected to cover the entire front, from neck to groin, not from neck to abdomen, and referred to the swelling of the belly as well, for, when we breathe, it also expands. Thus, in Russian, grud’ “breast” (with cognates elsewhere in Slavic) is related to Latin grandis “big, large, ample, great.” Aristoteles’s Greek thorax designated the whole “trunk”; “breast, chest; breastplate” are the word’s later senses. It is no wonder that, when bosom and breast collided, their meanings became more or less specialized.
The bosom is soft, while the breast makes one think of ribs. To clarify this meaning, languages have words and phrases like German Brustkorb, literally “breast basket,” and Russian grudnaia kletka [stress on na] “breast case.” Engl. chest is an old word. A borrowing of Latin cista, for a very old time it meant only “box, coffer” (compare a chest of drawers, tool chest, and simply chest “coffer”). Chest “thorax” first turned up in the sixteenth century. So now we have a pain in the chest, press a child to our breast, and let our bosom heave with uncontrollable sobs. A hairy chest is what many men live with, a hairy breast is a fact of life, but a hairy bosom is impossible. Yet in many cases, all three words are interchangeable. Only thorax, borrowed in the sixteenth century (just when chest acquired its new meaning), remains a special term.
Image credits: (1) Tree silhouette. CC0 via Pixabay. (2) Simplified language tree in Swedish by Ingwik. CC0 via Wikimedia Commons. (3) Joshua 1:1 in the Aleppo Codex. 10th century. CC0 via Wikimedia Commons. (4) Lord Byron, a coloured engraving. CC0 via Wikimedia Commons. (5) Tivoli, Villa d’Este:fontana di Diana Efesina, detta dell’Abbondanza. Photo by Lalupa. CC BY 3.0 via Wikimedia Commons.