Words That Sound Like Opposite But Are Actually Synonyms

English is not a fixed language so with time, words tend to come in more often and become acceptable.
These words are commonly called pseudoatonmys

1. FLAMMABLE/INFLAMMABLE

Looking at the above words, first thing that comes to the mind is, one catches fire and the other doesn't. Actually they mean the same thing.

2. BAR/DEBAR

Bar being the act of prohibition, funny enough debar also means the same thing.

3. REGARDLESS/IRREGARDLESS

Regardless, prevailing against odds and circumstances. Irregardless is likely originated from a combination of 'irrespective' and 'regardless' and thus became accepted.

4. HABITABLE/INHABITABLE

Habitable simple implies Suitable to live in. You would think inhabitable was any different, but it means the same thing.

5. GENIUS/INGENIOUS

Everyone has probably heard of genius. Clever, inventive person, and exceptional intellect. Ingenious also implies the same thing.

6. TERMINATE/EXTERMINATE

To terminate, the act of bringing to an end of something. Your guess would be with the prefix of 'ex' there would be difference but it does almost mean the same thing.

7. RESTIVE/RESTLESS

Your first opinion of restive would be in a state of rest, but restive actually means being unable to stay silent or still, thereby restlessness.

8. VALUABLE/INVALUABLE

Valuable means of great worth. Invaluable also means the same thing, being useful and indispensable.