What are some words where the "opposite" one means the same thing?

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!