ENGLISH is an immensely rich language, by far the richest the world has ever known. My single-volume dictionary claims that it contains 265,000 definitions, and thousands of new words and usages are added to the language every year.
No single person can know all of these, nor would it do him much good if he could because nobody else would understand him. Then what is the use of a language which is so rich? If you look at a good dictionary, you will find several different types of words listed.
Words in current use.
Obsolete words which you might need to understand long-dead writers.
( perdie, sapid ) Technical vocabulary which only a small sector of the population would understand.
( perchloric, perdendo ) Regional vocabulary which is only used in one country or region.