'bristleless' originates from the Old English word 'bristel', where 'bristle' meant 'stiff hair'. The suffix '-less' is used to indicate the absence of something.

'bristle' changed from the Old English word 'bristel' and eventually became the modern English word 'bristle'.

Initially, 'bristle' meant 'stiff hair', and the addition of '-less' indicates the absence of such hairs.