Bemused & Nonplussed: Here we have two words that have traditionally meant something like 'bewildered' or 'perplexed,' but they've each veered off in different semantic directions -- one towards resolute calmness (nonplussed) and the other towards mild amusement (bemused).

Disinterested: This word and uninterested are often used as synonyms, but they're not quite the same. To be uninterested is to have no enthusiasm for something, while to be disinterested is to have no bias. For example, if you were on trial, you'd want an unbiased, disinterested judge, not one who was bored by your case.

Flammable & Inflammable: Unlike the other word pairs on this list, these actually mean the same thing even though they're often mistaken for antonyms. Since the early 20th century, flammable has been the preferred spelling. According to Grammarist, "[b]ecause this confusion can have dangerous real-world consequences, the shift from inflammable to flammable is welcome."

Nauseous & Nauseated: One means to cause nausea and the other means to experience it, but do you know which is which? If someone is feeling sick, they're nauseated.

Moot: You've probably heard the phrase "It's a moot point," meaning that the issue isn't worth discussing. The primary definition actually describes a topic or question that's open for discussion, but which may be theoretical or academic.

Ultimate: This word gets trotted out as a synonym for "extreme" or "best of the best," but it originally meant the last or final occurrence of something.

Enormity: Most people think this word describes something huge or momentous. It makes sense--enormity sounds a lot like enormous, after all -- but its primary definition is not bigness but badness. Merriam-Webster defines it as "a shocking, evil, or immoral act" or a "great evil or wickedness."

http://www.huffingtonpost.com/gramma...ushpmg00000063