“The difference between the right word and the almost write word is the difference between lightning and a lightning bug.” – Mark Twain
Choosing the right word is essential. Synonyms are great, they help add variety to writing and make our language more dynamic, but two words don’t always have the exact same meaning. Searching at dict.org can result in the Moby thesaurus, a group of related words, not necessarily the same same, one cannot simply select one and move on, though I imagine if you used it to substitute words, you could come up with some crazy stories.
A good example is the Eye of Argon. In it the author is writing about a barbarian, think Conan fanfiction. A loincloth is an essential part of being a barbarian; looking at thesaurus.com’s “visual thesaurus” at the bottom, g-string is closely related. Like a loincloth, a g-string essentially covers the same area. Yet one would not use it when referring to a barbarian, as the author did. Sorry for the image of Arnie/Conan in a lacy g-string.
Similarly, there is the use of the wrong word, known as a malaprop, the unintentional misuse of a similar sounding words. I know I’m certainly guilty of this in conversation.
Another aspect is mispronouncing a word, like epitome, it’s not ep-i-tow-m. It’s great to watch someone use words they don’t know how to pronounce, especially when they’re acting smarter than they really are.