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!
While checking words that might work here i was reminded of this annoying trio:
They mean, respectively:
also elucidate more common in scientific works,foreshadowing.