'unsaddle' originates from the Old English prefix 'un-' combined with the noun 'saddle' (Old English 'sadol' or 'sædela'), where the prefix 'un-' conveyed reversal or removal and 'sadol' meant 'seat for riding'.

'sadol' (Old English) changed to Middle English 'sadel'/'saddle', and by prefixing 'un-' in Middle English the verb 'unsaddle' was formed, eventually becoming the modern English word 'unsaddle'.

Initially it meant 'to remove a saddle from (an animal)', and over time this core meaning has remained largely the same in modern usage, with a secondary sense of 'dismount'.