hill:A natural elevation of the earth's surface rising more or less steeply above the level of the surrounding land. Formerly the general term, including what are now called mountains; after the introduction of the latter word, gradually restricted to heights of less elevation; but the discrimination is largely a matter of local usage, and of the more or less mountainous character of the district, heights which in one locality are called mountains being in another reckoned merely as hills. A more rounded and less rugged outline is also usually connoted by the name.——Oxford English Dictionary

hill:an area of land that is higher than the land around it, like a mountain but smaller.——Longman Dictionary of Contemporary English  @en