Celtic *dra(:)wā 'ryegrass' (updated)

Celtic *dra(:)wā 'ryegrass' is found in dialectal French droue, druive as well as other similar forms in Gallo-Italic (e.g. Lombard droga). Brittonic languages (Welsh drewg, Breton draok, dreok) reflect a suffixed form *drāwā-kā 'darnel (Lolium temulentum)', also found in Late Latin dravoca, continuated in Gallo-Romance *dravocāta > French dragée 'forage'¹ (not to be confused with its homonymous 'bonbon' or 'tablet')². 

IE cognates of the Celtic word are Germanic *tarwō, found in Middle Dutch tarwe, terwe 'wheat' and English tare 'weed; vetch' (also used in translations of the Bible to name a type of ryegrass, probably darnel), as well as Baltic *dirwā 'field', Slavic *derevna 'arable field, village'. From these forms, Indo-Europeanists reconstruct a protoform *derH2u- 'a k. of wild cereal', which in my opinion belongs to the lexicon of Mesolithic hunter-gatherers, with a semantic shift in some languages due to the adoption of agriculture in the Neolithic, a process called acculturation.

This word has cognates in Altaic: Turkic *dạrɨ-g 'millet', Mongolian *darki ‘brushwood’, Tungus-Manchu *daragan 'quitch; reed, cane', Korean *tār 'reed', pointing to the initial consonant being an ejective *t’. 
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¹ The French word for 'darnel' is ivraie, from Latin ēbriaca (f.) 'intoxicated'. There's also dialectal Basque libraka (R), with agglutination (proclisis) of the definite article. 
² X. Delamarre (2008): Dictionnaire de la langue gauloise, p. 147-148.