'aren't' originates from English, specifically a contraction of the words 'are' and 'not'.

'aren't' developed in Early Modern English by contracting 'are not' (appearing as 'arent' in some 17th-century writings) and later became commonly written with an apostrophe as 'aren't'.

Initially it meant 'are not' (the negative of 'be'); over time this core meaning has remained essentially unchanged, though its written form (with or without an apostrophe) has varied.