Word Origin & History
hillO.E. hyll, from P.Gmc. *khulnis (cf. M.Du. hille, Low Ger. hull "hill," O.N. hallr "stone," Goth. hallus "rock," O.N. holmr "islet in a bay," O.E. holm "rising land, island"), from PIE base *kel- "to rise, be elevated, to be prominent" (cf. Skt. kutam "top, skull;" L. collis "hill," columna "projecting
object," culmen "top, summit," cellere "raise," celsus "high;" Gk. kolonos "hill," kolophon "summit;" Lith. kalnas "mountain," kalnelis "hill," kelti "raise"). Formerly including mountains, now usually confined to heights under 2,000 feet. Hillock (1382) preserves M.E. dim. suffix -oc. Phrase over the hill "past one's prime" is first recorded 1950.
"In Great Britain heights under 2,000 feet are generally called hills; 'mountain' being confined to the greater elevations of the Lake District, of North Wales, and of the Scottish Highlands; but, in India, ranges of 5,000 and even 10,000 feet are commonly called 'hills,' in contrast with the Himalaya Mountains, many peaks of which rise beyond 20,000 feet." [OED]