Among teachers of English at school-level, using a thesaurus is a Good Thing, being a means of enlarging children's vocabulary. But a ticked box for the maximum number of different words on the page is a poor substitute for teaching genuinely good writing, so among serious writers, and teachers of writing, using a thesaurus is often spoken of as a Very Bad Thing. And when you consider the thesaursed version of "Twinkle, Twinkle, Little Star", which floats round the internet attributed to John Raymond Carson, you can see why:
Scintillate, scintillate, globule vivific,
Fain would I fathom thy nature specific.
Loftily poised on the ether capacious,
Strongly resembling a gen carbonaceious,
In the mix of this argument is also the human tendency to equate long and obscure words with greater intelligence, superior education, higher status and more serious purpose. Since most human writers have a contrary streak, and others simply wear their snobberies upside-down, we tend to resist that common tendency by instead equating short and familiar words with greater authenticity, wider appeal, more serious meaning - and often greater intelligence, because when you're trying to express a complex idea in simple, non-specialist language, there's nowhere to hide your own lack of understanding.
And yet ... There isn't a writer in the world, I'm sure, who hasn't hit that moment of knowing there's a better word for what we want to say, but not being able to bring it to mind. That word, twinkling or gurning away just out of sight, is a more accurate, apposite, familiar or strange word; a word with a better bouncy rhythm, rounder vowel-sounds, or clinkier consonants; a word from deeper in the gutter or higher in the heavens, from the Bible or the Beats, from Preston, Periclean Athens, Pangaea or Pluto. And if you could use a thesaurus, you might be able to remember it.
First rule of using a thesaurus: there is no such thing as an exact synonym. Of course, that fact is central to what we do: use the exactness of our words to control our readers' understanding and response. I've been known to say that I can teach anyone to write better if they have some sort of feeling that cross/angry/irate/annoyed/irritated/furious/outraged don't all mean the same thing.
The thing is, another human tendency, given similar words, is to use them to make finer distinctions among what they denote. This evolutionary process is fundamental and inevitable: if Anglo-Saxon cū and Norman-French beof meant exactly the same thing on 14th October 1066, they didn't do so for long. And evolution doesn't happen just in the denotation that kept cū wandering around eating grass, while beof began to turn up on a platter with Yorkshire pudding. It also happens in the connotations, as demonstrated by the idea that your cow of a football teacher is beefy enough to be frightening.
Connotations form the halo of further meaning that every word carries: the nuances and implications, the things you imply by using it, the things the reader infers by your use of it, the echoes and references from liturgy and literature, myth and the Daily Mirror. It's the connotations, on the whole, that make every word "say" something about its user: not just who they are in age, gender, ethnicity, class, personality and emotional state, but their purpose in using it. Is the word you've found not just the right word for this story, but for its user? What's more, over the centuries and even decades both denotations and connotations can shift radically, so if you're writing something not set in your own time, you have two sets of denotations and connotations to integrate: those of Then, and those of Now.
So I suggest that, when you look in a thesaurus, the one thing you're not trying to do is to find a word that means the same as the one you've already thought of. It's much wiser to think of your starting-word as a mere placeholder, a stand-in, a thing in square brackets, for the right word that you've wanted all along if only you could have brought it up from the vault.
And don't forget that the right word isn't necessarily something longer, fancier or more obscure: it might be simpler. This is particularly true if you - like many aspiring writers - have trouble shedding the office-speak when you leave the office: so often "aspirations" would be better as "dreams", and "a disastrous eventuality" as "a car-crash", and a thesaurus is a good way to remind you of it.
On the other hand, teachers of writing know all too well the story which has clearly been written by auto-thesaurus, and I expect there's even an app out there: every word is roughly right but slightly off-key, and the mixture is not just discordant, but positively cacophonous. So, how do you make sure your story doesn't get thesaurused to death?
I think the test is to keep alert to what you intuitively feel - even before you consciously think - when you see the words that the thesaurus offers. I'd divide the possible reactions thus:
"Duh! Of course!" Use the word. You knew it all along, and it almost certainly has all the right sounds and meanings for what you're trying to say. Although checking these things is never a bad idea.
"Ooh, tasty, hadn't thought of that!" Be careful. It might please you as a word in itself, but unless you're confident that not only the denotation, but the connotations, are what you want, things could go very wrong. I have some students, often good writers in other ways, whose manuscripts' margins are full of me saying "Infer means 'assume' or 'deduce', which which I don't think you mean here. Imply?". They picked the word that sounded more interesting and roughly right, without understanding its meaning fully.
"Interesting. I don't know that one!" Almost certainly don't use it. Even if you check its meaning in a dictionary, chances are you won't use it with the right nuances and rhythms. It won't sit naturally in voice of character or narrative.
If you do go for a word the thesaurus offered, I suggest you move on from there to look it up very stringently in something really comprehensive, such as the full online Oxford English Dictionary, which you should be able to get access to via your public library, maybe even from home. That's not just because you might be wrong about the word's meaning, it's also because chewing on this new or recovered word is an excellent way to start integrating it into your fully-understood word-hoard.
And finally, a couple of thoughts about thesauri (which The Oxford Dictionary for Writer and Editors says is the correct plural, though some sites suggest that thesauruses is also just fine):
- The free online ones can be good for a quick check, but aren't nearly as comprehensive as a good print or paid-for-online one: again, don't forget that your public library should give you access - very possibly remotely - to the major sites.
- A thesaurus built on Roget's principle, with words collected together by concept, rather than dictionary-style, is far, far more useful: the next-door headers are words which are conceptual cousins to the one you're starting with, so browsing is far more fruitful than the random neighbours the alphabet creates.
- For what it's worth, I have the big Bloomsbury Thesaurus, in the new edition which was published in 1997. It's Roget-style, and for my money is the best; it can still be found second-hand, and I bless the day I bought it. It also had lots of very useful boxes of vocabulary for specific things - shipbuilding terms, musical terms, breeds of horse, or astronomical bodies - which is subtly different aspect of the word-you-can't-quite-remember problem.
- And don't forget with all sites and all words to apply your "Is this British English or American English or something different again?" scanner. Even when the denotation is exactly the same, the connotations are almost certainly not.