According to the traditional view, English knife, from Germanic *knība-z 'knife' (with no native IE etymology), is a Wanderwort which spread from Old Norse into Old English and other Germanic languages, as well as Old French quenif, quanif 'pocket knife', (and in diminutive form) Occitan ganivet, Aragonese cañivete and Basque kanibet, ganibet, kanabita, gaiñibeta, ganabeta, kanit, gaminta 'penknife'.
However, the German linguist Theo Vennemann1 (see my earlier post) reversed the propagation direction, considering Basque kanibet to be the original form, as a compound of kana 'cane' (a loanword from Latin canna) and bedoi 'pruning shears'2, a dialectal word of limited extension. But (unknowingly to him) the latter is a loanword from Gaulish uidubion 'hoe' (glossed as Latin vidubium), a compound from uidu- 'wood' and -bion < Celtic *bi-na- 'to hit, strike' < IE *bhejH-. This root is reflected in Germanic as *bī́ɵla-, *bīdla- 'knife, sword, ploughsare' > English bill.
My own proposal is that Latin novācula 'razor, knife' (Portughese navalha, Spanish navaja, Catalan navalla, Aragonese novalla) < *kne-wa-tlā, traditionally derived from IE *ksew- 'to rub, to whet'3, is actually a reflex of IE *kneH2- 'to scratch, to scrape'. This etymology can also explain Basque nabas- 'plough' (in compounds)3 < *knā-wa-z and Germanic *knība-z < *knē-wa-z as borrowings from some IE language (possibly Italoid) where IE *w gave b.
The semantic shift from 'knife' to 'plough' can also be observed in the descendants of Latin culter 'knife' > Occitan coltre, French coutre, Italian coltro 'ploughshare', Basque golde 'plough', the original meaning being transferred to the diminutive cultellum > Galician coitelo, Spanish cuchillo, Catalan coltell 'knife' (the latter form being displaced by ganivet).
Another interesting Basque word is saratu 'to hoe', a loanword from IE *sºrp-'sickle; to cut' (Latin sar(r)iō 'to hoe (vine)' < *sarpiō.) ______________________ 1 Zur Etymologie der Sippe von engl. knife, franz. canif, bask. kanibet*, in Europa Vasconica, Europa Semitica (2003), pp. 427-452.
2 Also Bearnese bedui. See García de Diego, Diccionario etimológico español e hispánico (1985), pp. 1063-1064. 3 Considered by many Indo-Europeanists to be an extension of IE *k´es- 'to cut'. 4 There is also the Bearnese hapax naves '(large) knife'.