'barroom' originates from Modern English, formed as a compound of the words 'bar' and 'room'; 'bar' ultimately comes from Old French 'barre' (from Late Latin 'barra') where 'barra' meant 'bar, barrier', and 'room' comes from Old English 'rūm' where 'rūm' meant 'space' or 'room'.

'bar' entered English via Old French 'barre' and developed in sense from a physical barrier to an establishment serving drinks; 'room' comes from Old English 'rūm' and passed into Middle English as 'room'. The compound 'barroom' arose in English (notably in the 19th century) to denote the interior room of a bar.

Initially it meant 'a room in which there is a bar' (a literal interior space); over time it also came to describe the bar's atmosphere and is used attributively (e.g., 'barroom brawl') to imply rowdiness or violent encounters.