noun, feminine/uj/plural: houilles
stone coal, mineral coal
Related: gaz de houille
From Old Walloon (Liégeois) hulhes ( > modern Wallon hoye), probably from Frankish *hukila (“pile, mound”), a diminutive form (compare dialectal Dutch heukel), ultimately from Proto-Indo-European *kewp- (“to arch, bend, curve, vault”), see also Proto-Germanic *huppōną (“to hop”), *hufą (“elevated place”).