What language has the most words? Fred Karlsson, who is a Professor of Linguistics at Helsinki University, says it's English. There are more than 600,000 entries in the Oxford English Dictionary. Some US scholars reported in last December's Science magazine that there were almost another 600,000 words that weren't included in the dictionary.

The number of English words also increases more rapidly than that of any other language. During the past 50 years, an average of 8,500 words have made their way to the English language every year. The vocabulary increases because English is the most important international language of science. The man in the street doesn't of course know the vast majority of these words.

However, if "the number of words" is understood to mean all the various inflected forms a word can have, Finnish fares very well. The number of Finnish nouns alone exceeds 140 million - and that is a modest estimate.

One can get by with a small vocabulary, though. A long time ago I read an article that said the average Briton used about 500 different words in his daily conversation with his friends.

A claim that any modern language has ten times more words than any other modern language is clearly based on immensely flawed information.
You may find this article interesting http://iteslj.org/Articles/Cervatiuc-VocabularyAcquisition.html

BTW, is there a way to reliably estimate a person's vocabulary?
Students: Are you brave enough to let our tutors analyse your pronunciation?
Thanks for the link, Ivanhr. I read the article with interest. I know nothing about estimating the number of words people know.

I agree that it's likely English, in terms of uninflected forms. We have a pretty unwieldy number of adjectives and nouns to describe so many archaisms and abstract concepts. When other languages try to approximate some of our nouns, they sometimes requires an entire phrase.
I really can't believe what this professor said about something that is so obvious. The greek language is the richest language in the world by far with 5 million words and 70 million word types according to the 1990 Guinness Book of Records, while the English language has only 490.000 words. This means that greek has 10.2 times more words than english. Mr Karlson, 30% of the words you are using when speaking english are greek (3 out of 10 words). You speak greek you just don't know it.

P.S: I'm German
Students: We have free audio pronunciation exercises.
 fivejedjon's reply was promoted to an answer.

Indeed. The Greek language is the richest language in the world, even stated by the Guinness book of Records with 5 million words and 70 million word types. And that is not so strange actually.

-Greek language is the oldest attested continuous living (indo-European) language in the world from 15 century BCE onwards. https://en.wikipedia.org/wiki/Indo-European_languages#/media/File:IndoEuropeanTree.svg


-It's also the first world language that connected the ancient world. At some point even people in Arabia and Africans where speaking Greek. More specifically Koine Greek, meaning Common Greek. The Greek language radically changed languages in many ways. The bottom line was that the Greek language was and could be read and spoken by all kinds of peoples and populations in also a much more simpler ways. While for instance in Egypt
only priests and a very small selection of people could understand to read and write in their own language.

-Greek being the oldest attest living continuous language in the world, and the richest with 5 million words, and being the first world language. Let add on top that Greek civilization is one of the, and cited by many the most influential civilization in the world today that impacts our modern societies in so many ways. Greece is the foundation of the Western world which dominates 60% of the world, and with vast remaining influences to most of the remaining parts of the world. That Greek civilization, aside from it's big impact to world civilization today, is but a time period of a much grander history. Greek history spans all the way to the dawn of human civilization. Greece has over 1000 archaeological sites dated in the Neolithic, and has a vast extensive bronze age with 3 full bronze age civilizations: The Cycladic civilization (3300-2000 BCE), The Helladic Period (3200-1200 BCE), Minoan Civilization 3650-1400 BCE, and the Mycenaean civilization 2000-1200 BCE. After Classical Greek period of 800- 65 BCE, history went further as the Greek empire of Byzantium which lasted from 300 AD - 1453 AD, untill the fall of Constantinople.
Now I mention all of this in a breath, because the world records that the Greek language holds, and it's incredibly deep history with civilizations with countless of inventions, contributions to our world today, reflects the reason why the Greek language consists of 5 million words and 70 million word types.

And we all know that Greek is also the foundation language of the Scientific, Astronomical, Geographic, Medical world. Even the name India is but a Greek word. And even 5000 peoples names in western civilization are Greek.

So all in all. The records of the Greek language are incredible, but true and equaled by the deepness and richness of it's history and civilization that is the foundation of our society today.
And even today many new Greek words are created in so many levels of our society and sciences.