For example, “flammable” and “inflammable” both describe an object that can easily catch on fire. I can also think of “ceased” and “deceased”, both of which can mean someone or something has been brought to an end.
edit: Some people are including words that can also mean its opposite (like sanction or table), those are cool too! The more weird words, the better!
Rent and lease are not opposite. They mean the same thing in both contexts and describe both sides of the relationship.
The first definition means the same thing for both words. The second definition also means the same thing for both words.