waywiser
/ˈweɪˌwʌɪzə/noun
1An instrument for measuring and indicating distance travelled, especially by road; specifically a pedometer or odometer. Now historical.
2A guide post. Also figurative. Now rare.
Origin
Mid 17th century; earliest use found in Robert Child (1613–1654), physician and agriculturist. From way + wise + -er, although the semantic motivation in sense 1 is unclear.