Words don't necessarily keep the same meaning. Simple descriptive words such as rain or water are clear and necessary enough to be unlikely to change. Other more complex words have often come on quite a journey since they were first coined:
chauffer (French) to heat; then meant the driver of an early steam-powered car; subsequently chauffeur
sine nobilitate (Latin) without nobility; originally referred to any member of the lower classes; then to somebody who despised their own class and aspired to membership of a higher one; thus snob
theriake (Greek) an antidote against a poisonous bite; came to mean the practice of giving medicine in sugar syrup to disguise its taste; thus treacle
Are there any others you can think of?