There are at least 250,000 specifically English words, many of them with dual or multiple meanings. Probably the same number of words from foreign languages, such as karaoke and spaghetti, have been incorporated without change into common English usage. In addition, new words are coined to meet the needs of the changing world – streamline when aviation became a feature of contemporary life, for example. Similarly, words become obsolete when they are no longer relevant. No one, not even the those who compile dictionaries, knows every one of them.
In general, people have a sizeable core vocabulary of everyday words that doesn't change much during their lifetimes. Then at any one time they have a usually smaller vocabulary of "favourite" words. The vocabulary of "favourite" words does change and new "favourites" take over.
In addition, there are specialist words used by professionals, such as doctors, lawyers and engineers (among many others). Slang and jargon, which change very frequently, and local dialect words, which tend to stay the same, are further additions.
No matter how highly educated and articulate, everyone is going to encounter unfamiliar words in this richest of languages. That is not a reason to reduce what is said to its most basic, especially if the concept under discussion is a complex and subtle one. Equally, using many words where few are adequate, long or obscure words when one word, a short word or a familiar word is just as good in order to sound important or clever is just pompous.