The ideal tool for people who love reading but are too lazy to take the time to actually learn the language, keeping one of these at the side of you can really help you to understand a text. It’s nothing to feel embarrassed about when you come across a word you don’t understand, a friend once told me that the unabridged English dictionary ran into something like 24 volumes, all of them thick and heavy enough to break a strong man’s neck if he was foolish enough to attempt to use one as an aid to his learning how to walk like a posh lady. Nobody learns all the words, not unless they have some kind of creepy language fetish, it just isn’t worth it. Instead we (hopefully) learn just enough of the language to communicate what we want to say to the people around us, and understand most of what it said to us by others. It’s nice to be able to describe a person as a “peerless example of malevolent artifice”, but quite sufficient just to call them a nasty piece of work.
So there’s no shame in being unable to understand a word, it doesn’t reduce your ability to reason or the validity of your opinion and certainly doesn’t mean that you’re stupid, no more than would your not having learnt to speak Russian or understand astrophysics. Breakfast Club is a great movie, but watching it isn’t the only good way you can spend an hour and a half of your life.
But, just as learning Russian would enable you to communicate better with a larger pool of people, and astrophysics your understanding of the mechanics at work in the universe, expanding your vocabulary opens up a wider range of texts for you to enjoy and study, many of which are rather good. And you’ll find that certain words you come across will keep cropping up again and again in books, on TV and in conversations with certain people or groups. You learn them once, taking maybe a few seconds for each, and you’ll be equipped to understand them forever. It can be well worth the time.
The previous 3 paragraphs have been addressed to readers, if you’re a writer and hope to become a good one you will need to make use of dictionaries, thesauruses, or some kind of vocabulary building aids. Words are the tools you use to share your soul with the world, which would still be damned near impossible even if you sold it to the devil for the time to memorise all those 24 volumes. The tragedy of the artist is that they can only paint with the colours that appear in light’s spectrum, it’s bad enough that you’ll never get to stain a canvas with the colours inside of your head, don’t try to do it without red and yellow as well.