An antonym is a word that's opposite in meaning. So the correct option in regards to the given question is option "D". Synonym is the opposite of antonym. Synonym means similar in meaning or rather same in meaning. The example of antonym are likely and unlikely, fortunate and unfortunate, able and unable etc. There are numerous examples in English literature that are opposite in meaning to a given word. I hope this has been of use to you and will help you in future.