'antechoir' originates from French, specifically the word 'antechoeur', where 'ante-' meant 'before' and 'choeur' (from Latin 'chorus') meant 'choir'.

'antechoir' passed into English via Middle French 'antechoeur' and Middle English kept the form 'antechoir', eventually becoming the modern English 'antechoir'.

Initially it meant 'the area before the choir' and that basic sense has been retained into modern usage.