Term for words that seem like opposites but actually mean the same thing?

Is there a term for words that seem like they should be opposites, but are actually synonyms?



False Antonyms or Pseudoantonyms.

As opposed to Sanction, which is an Autoantonym (it means the opposite of itself)

Now that the OP has been answered:

I’ve never heard the term “autoantonym” but have heard words like sanction and cleave referred to as contranyms (although autoantonyms makes sense as well).

“Dust” is another

When I was growing up the word was “inflammable”, capable of being inflamed. Too many people took the “in” as negation and so “flammable” became standard in the interests of safety. But now, “inflammable” was ambiguous. What used to be “non-flammable” is now generally rendered as “inflammable”, although I think “non-flammable” would be clearer, given this history.

“Cleave” is not really a contranym (the word I am familiar with). It is two words with different origins and etymologies that, after sound changes, have fallen together. The first one, cleave, cleaved, cleaved means put together and I think is likely cognate with glue and collate. The other, cleave, clove, cloven (or cleft) means to separate. I think a garlic clove is a piece separated from the head.