Old English rum "space" (extent or time); "scope, opportunity," from Proto-Germanic *ruman (cf. Old Norse, Old Saxon, Old High German, Gothic rum, German Raum "space," Dutch ruim "hold of a ship, nave"), nouns formed from Germanic adjective *ruma- "roomy, spacious," from PIE root *reue- "to open; space" (cf. Avestan ravah- "space," Latin rus "open country," Old Irish roi, roe "plain field," Old Church Slavonic ravinu "level," Russian raviina "a plain," Polish rum "space"). Old English also had a frequent adjective rum "roomy, wide, long, spacious."
Original sense preserved in make room "clear space for oneself" (late 14c.); meaning "chamber, cabin" first recorded early 14c. as a nautical term, and first applied mid-15c. to chambers within houses. The Old English word for this was cofa, ancestor of cove. Room-service is attested from 1913; room-temperature from 1879. Roomth "sufficient space" (1530s) now is obsolete.