1A book of maps showing the roads of a district or country, often having additional information of interest to travellers or motorists; (also formerly) a book describing particular roads or routes.
Now frequently in the titles of such books.
2A narrative of a journey by road, especially a journey that alters a person's outlook on life. Also occasionally: a logbook kept by the driver of a commercial vehicle.
Early 18th century; earliest use found in John Scheuchzer (1702–1729), physician and naturalist. From road + book.