Let me let you on a little secrete. No two words mean exactly the same thing. You might, at first glance, think that the adjectives “hard” and “difficult” are perfect synonyms, but they’re not. I know you don’t believe this but a little example will help. Can we swap these adjectives in an example like “hard surface” and still maintain the same meaning? “Difficult surface” sounds so wrong that it triggered all the linguistic filters in my brain. This is why it is well established that perfect synonymy does not exist. And this is a good reason for you to be careful choosing your words. Just because the thesaurus lists two words as synonyms doesn’t mean that you can simply slot one in for the other. Here are the most common ones.