'well-marked' is a compound word formed from 'well' (meaning 'in a good or satisfactory way') and 'marked' (the past participle of 'mark', meaning 'to indicate or make noticeable').

'well-marked' was formed in modern English by combining 'well' and 'marked' to describe something that is clearly indicated or defined.

Initially, it meant 'clearly marked or indicated', and this meaning has remained consistent in modern usage.