Sometimes a word can have two contradictory meanings. For instance, the word "sanction" can mean "to allow or permit" or "to prohibit or penalize". Every day in the news we hear of some country or entity being the object of sanctions. If I were to say that I sanction some sort of behavior it would most likely mean that I allow the form of behavior indictated. Another example that comes to mind is the word "host". In Early Modern English this word meant "army", as in "the heavenly host", but now it means one who receives a guest. From the earlier meaning we get the word "hostile". Can you think of other words that have two opposite meanings in one word?

"Prove" has reversed meaning over time, as can be seen in the expression "the exception that proves the rule."

I thought there were two meanings of "host" that each derived from different words. I also can't remember for the life of me what "exception that proves the rule" really means. Oh well, it's been a long day, whatever.

host "army" and host "one who entertains guests" are related. guest is also related.

Rent, lease, sublet, etc. are confusing in that the subject can be at either end of the transaction. They can be clarified with a prepositional phrase (e.g. "He's renting the house to a lawyer and her husband") or a particle ("He's renting it out"), but just a bare sentence like "He's renting it" is ambiguous.