Some advice will tell you that if you have to look a word up in the thesaurus, then it shouldn't be in the story.

I like to think that that advice is more suggesting that you should choose your words carefully. There are a lot of writers who decide they're tired of saying, say, "GREEN EYES" all the time, so they punch in the words, see some substitutes, and toss 'em into their manuscript. Then editors and agents read sentences like:

Embarrassment coloring his cheeks, Tom's verdigris peepers dipped towards the floor.

The jig was up. Madeline quickly decamped.

And they go off on rants about the innocent thesaurus. If your characters have walked so many times that you feel the need to change the word, maybe you need to consider describing other things besides the motion of legs.

And writers told that "decamped" sounds weird will reply: No, no, I used it right. It means to depart, duh.

That may be true, but you need to make sure the word fits in the story. When in the market, chefs choose the right cuts of meat for their dish. They take the time to make sure they've picked the right melon for dessert.

Here are some things to remember the next time you go word shopping.

These examples are for synonyms, since that's the main problem, but apply to antonyms as well.

Synonyms are considered to mean roughly the same thing and be acceptable, interchangeable alternates with each other.

However, word choice can set the tone of a scene, among other things, and the replacement might not have the same ring to it.

A dying man has a lust for life. An excitement for life. A carnality for life. An appetence for life. A hunger for life.

Words you find in the thesaurus aren't always ready to be plugged into the hole in your sentence. You might have to conjugate them or alter the sentence.

Home from the beach, your son walks into the kitchen with sandy feet. Your daughter follows with granular feet.

Lucy might be better off strolling though and leaving granular footprints behind.

Flow is an often forgotten part of storytelling. The seasoned writers know all about it, but it's usually what trips up the inexperienced crowd. It's subtle, it's the way you read one sentence into the next...And overall it can be extremely difficult to do well over the entire course of a novel.

BUT almost everyone knows when flow is absent. Like your gutters, you want your story flowing freely. When leaves, acorns, and whatever else above your roof gets stuck in them, a blockage occurs. Readers remember they're reading. A word, sentence, or phrase trips them up.

One primary source of blockages is misused words. Just like the ones you find in the thesaurus.

They might make sense on a definition level, but word choice is also dependent on the storytelling. If a writer consistently writes in simple terms and phrases and descriptions, whipping out an advanced word may be jarring.

Example:

Laura slipped the collar onto the dog and attached the leash. Once she was certain that he wouldn't escape, she started to walk. Slowly. Just slow enough that he wouldn't feel the urge to run. The last time she'd walked Jupiter, he'd broken her nose chivying a squirrel.

"Chivy" isn't that obnoxious here, but you can see that in the paragraph, it's surrounded by basic words. The more the story is composed in simple terms, the more people tend to think that the writer is trying too hard when a complex word appears.

Just think about if I'd used something like magniloquent or puerile. What if the girl walking her dog suddenly looks up at the argent orb of night (the moon)?

There is a situation where a more technical term applies, but you don't know what it is. —-> You might be better off searching the internet, but sometimes you just need a refresher and the thesaurus can provide that.

The current character narrating or speaking has a different vocabulary/word usage. —-> The slave with no education might not be up to par with her scholarly master.

The word you used NOT the right one and you're looking for a better match. —-> Ink permanently darkened Ethan's shirt. Dirtied....sullied...Stained.

The word you're looking for escapes you. —-> Blood is leaking out of the wound...what is it doing? Bleeding, ah.

You're looking for an alternate way to say something. —-> Not everyone can be a walking thesaurus. Just use it wisely!