'barndoor' originates from English, specifically the combination of 'barn' and 'door', where 'barn' originally meant 'a place to store grain' and 'door' meant 'an opening that can be closed'.

'barn' comes from Old English 'bern' meaning 'storehouse' and 'door' comes from Old English 'duru' or 'dor'; the compound 'barn-door' developed in Middle English to denote the door of a barn and later appeared in modern English as 'barndoor' or 'barn door'.

Initially, it meant 'the door of a barn'; over time the term was also applied metaphorically and technically (for example, to the hinged flaps used on lighting fixtures), giving it an extended modern usage.