'westbound' originates from the combination of 'west' and 'bound', where 'west' refers to the cardinal direction and 'bound' means 'heading towards'.

'westbound' evolved from the Old English word 'west' and the Middle English word 'bounden', eventually becoming the modern English word 'westbound'.

Initially, it meant 'heading towards the west', and this meaning has largely remained the same in modern usage.