plain noun

ADJ. open The horses galloped across the open plains. | rolling, sweeping miles of rolling plain, made fertile by the river | great, unbroken, vast | flat | fertile fertile plains suitable for farming | grassy | coastal

PREP. across a/the ~ Cattle move freely across the grassy plain. | in a/the ~ the Olduvai Gorge in the vast plain of Tanzania | on a/the ~ Nothing grew on the plain.