The word knife came up in one of the recent comments. I have spent so much time discussing sharp objects (adz, ax, and sword) that one more will fit in quite naturally. The word that interests us today turned up in late Old English (cnīf) and is usually believed to be a borrowing of Old Norse knífr (both ī and í designate a long vowel, as in Modern Engl. knee). The word occurred in Old Frisian and Old Low (that is, northern) German in nearly identical or slightly different forms (for example, gnippe). Today, the cognates of knife are Icelandic hnífur (along with similar forms in all the modern Scandinavian languages) and Dutch knijf. We have seen that cutting tools may denote both house utensils and weapons. The same holds for knife. The Old Icelandic idiom deila kníf ok kjötstykki “to share knife and meat (pieces)” implies that knives were used for cutting food, but knífr also denoted a dirk, “such as the ancients wore fastened to their belts; and so a knife with a belt is frequently mentioned as a gift; the handles of these knives or dirks were neatly carved of walrus’ tusks” (this is a quotation from the great dictionary of Old Icelandic by Cleasby-Vigfusson). Slavic nozh- “knife” was sometimes glossed as gladius (“sword”) in old texts. Old Icelandic knífr also meant “penis,” obviously, a secondary meaning.
As could be expected, the origin of knife remains a matter of speculation. Lithuanian knêžas “knife” looks like Slavic nozh-, but with the enigmatic initial k-, as in knife. True to our rule not to explain obscurum per obscurius, that is, one word of undiscovered origin by referring to another “dark” word, we will, for the time being, remain on Germanic soil, though the temptation to find some cognates in Sanskrit, Greek, Latin, Celtic, and so forth is always great.
At first sight, the hypothesis I’ll cite below has little potential, but we will see that it is not fanciful. About a century ago, Edwin W. Fay, at that time a well-known specialist in Sanskrit, Greek, and Latin linguistics, was very active in the area of Indo-European etymology. He seems to be almost forgotten. Wikipedia does have an entry about him, but it is very short and gives no idea of the range of his activities. Those interested in a rather representative list of his publications, at least to the extent it concerns Germanic, will find it, among other places, in my Bibliography of English Etymology. Obviously, if knife has a non-Germanic cognate, it should begin with gn– (by the First Consonant Shift). Fay cited Greek genus “lower jaw,” allegedly from a root meaning “to cut.” He pointed out that the jaw with the teeth was the first cutting instrument and that Samson made use of the jawbone of a donkey for bloody slaughter. Several other scholars also tried to derive knife form a gn-root meaning “to cut.” Perhaps knife, or rather knífr, did at one time mean “cutter,” but those who have read the previous posts on sword, axe, and adz (see, for instance, the latest one for June 17, 2020) will remember the many rather uninspiring attempts to explain all of them as cutters.
We should rather concentrate on the phonetic shape of knife. A glance at an array of kn-words will take us to knob and its twin nob “head”, knop “bud,” knub ~ nub “a small lump,” knot, German Knopf “button,” and Knospe “bud,” among very many others (thus, various protuberances). It is hard to tell how many relatively recent words spelled with an n might once begin with kn-. Perhaps the underlying sense of knob and the rest was “swelling.” Close to them are Engl. knee and German Knochen “knee.” Unlike knot, knee has respectable relatives, with Greek gónu and Latin genu among them (genu is familiar to English speakers from genuflection). It seems natural to reconstruct the meaning of this root as “to bend,” especially because Greek gōníā means “angle.” However, a knee is also a kind of protuberance. Not incredibly, the kn-root in Knochen and elsewhere is sound-imitative, as in German knack “crack.” Nor is Engl. knack “skill at performing a difficult task” too far from knack “a sharp blow or sound.” Fay’s jaw, knee, German Knochen “bone,” and their kin are members of an amorphous mass, containing the names of vaguely similar objects.
Knife looks different, but it too belongs with several kn-words, and the goal of the previous excursus was to point out that the multitudes with which we are dealing have porous borders. Two German words spring to mind: kneifen “to pinch” and its regional variant kneipen. Other kn-words have different forms but mean approximately the same: Engl. knead, German knatschen “to crumple,” German knicken “to snap; fold, bend,” and so forth. We wade through this morass (knack, knick-knack, knock, knop ~ knob) and begin to realize that the words are eerily alike: they denote lumps, bones, small hard objects, blows, cracks, and so forth. We hardly detect a root there in the strict sense of this term. In such words, one rather senses an impulse, perhaps sound-imitative, perhaps sound symbolic: kn– and more or less arbitrary “supplements.” Say kn– and add whatever you want; people will understand you. This process goes back to antiquity. Outside Germanic, gn– performed the same function. Is knife one of such words? Perhaps. If so, it is, from an etymological point of view, not a cutter, but rather a crusher (Dutch knappen means “to crush”). Walter W. Skeat thought that knife is related to nip and nibble: compare Low German knibbeln and Dutch knabbeln (the same meaning).
Other suggestions about the origin of knife are not radically different from those we have seen—except one. It is usually believed that French canif “knife” is a borrowing from Germanic (possibly from Old English). The twelfth-century form was canivet, which to the unprejudiced observer looks like a diminutive form of the same word, with a inserted to facilitate the pronunciation of the unfamiliar group kn. Theo Vennemann, a distinguished German philologist and linguist, concentrated on Basque ganibet ~ kanibet “knife.” According to him, the word consists of two parts: kani and bet, both of which he analyzed in detail. This word, he believes, traveled to Catalonian and French and from the Basques to Germanic, including Old Icelandic. Knowing nothing about Basque, I’ll leave kanibet alone, though, I suspect that the proposed etymology is too complicated, and complicated etymologies seldom survive. Finally, to repeat, I am not sure why canivet could not be a diminutive of canif. Vennemann’s hypothesis is part of a much larger whole, for he believes in the existence of a significant Basque substrate in the modern European languages. This aspect of his reconstruction cannot be discussed here.
In my opinion, knife should not be separated from a host of other Germanic kn-words. Occam’s razor works very well in etymology. Knife, as it seems, was coined in Germanic, most likely, in Old Norse. It belongs with many words designating objects and actions that suggested knocking, pushing, bending, pressing, and so forth. Not improbably, all such words were “expressive.” From the Vikings the word became known in English, French, and Basque; Basque borrowed it in its diminutive form. We are in the dark about the attraction of the Germanic knife, but, given the movements of great masses of soldiers at that time, the names of various weapons could and did easily become common property.