strath
A wide, flat river valley.
[T]hoſe fair Straths that vvater’d are / VVith Tay and Tvveed’s ſmooth Streams, / VVhich gentily and daintily / Eat dovvn the flovvry Braes; / As greatly and quietly / They vvimple to the Seas.
A piece of flat land beside a body of water.
[T]he place is pretty pleasant, close by Forth waterside, att the foot of Craigmor, betwixt which and the watar there is a strath very proper for walking: […]
Where it comes from
Borrowed from Irish srath and Scottish Gaelic srath (“wide, flat river valley, strath; floor of river valley; river meadow”), both from Old Irish srath (“grass, sward; river valley; floor of river valley; river meadow”), from Proto-Celtic *stratos (“valley”), from Proto-Indo-European *str̥h₃tós (“spread; stretched”, adjective), from *sterh₃- (“to extend, spread, stretch out”). The meaning was likely influenced by a Cumbric/Pictish cognate; compare Welsh ystrad. Doublet of stratus.
Adapted from the Wiktionary entry strath (CC BY-SA 4.0).