How many words are there in the English language?

There is no single sensible answer to this question.

• It is impossible to count the number of words in a language, because it is so hard to decide what counts as a word.
• Is "dog" one word, or two (a noun meaning "a kind of animal", and a verb meaning "to follow persistently")?
• If we count it as two, then do we count inflections separately, too (dogs, plural noun; dogs, present tense of the verb).
• Is "dog-tired" a word, or just two other words joined together?
• Is "hot dog" really two words, since we might also find "hot-dog" or even "hotdog"?
• It is also difficult to decide what counts as "English".
• What about medical and scientific terms? Latin words used in law, French words used in cooking, German words used in academic writing, Japanese words used in martial arts?
• Do you count Scots dialect? Youth slang? Computing jargon?
• The Second Edition of the Oxford English Dictionary contains full entries for 171,476 words in current use, and 47,156 obsolete words.
• To this may be added around 9,500 derivative words included as subentries.
• Over half of these words are nouns; about a quarter, adjectives; and about a seventh, verbs; the others are made up of interjections, conjunctions, prepositions, suffixes, etc.
• These figures do not include entries with senses for different parts of speech; such as, "noun" and "adjective".
• This suggests that there are, at the very least, a quarter of a million distinct (250,000) English words, excluding inflections, and words from technical and regional vocabulary not covered by the OED, or words not yet added to the published dictionary, of which perhaps 20 per cent are no longer in current use.
• If distinct senses were counted, the total would probably approach 750,000 words.

Is it true that English has the most words of any language?

• This question is also practically impossible to answer, for the reasons indicated above; however, it seems quite probable that English has more words than most comparable world languages.
• The reason for this is historical. English was originally a Germanic language, related to Dutch and German, and it shares much of its grammar and basic vocabulary with those languages; however, after the Norman Conquest in 1066, it was hugely influenced by Norman French, which became the language of the ruling class for a considerable period, and by Latin, which was the language of scholarship and of the Church.
• Very large numbers of French and Latin words entered the language. Consequently, English has a much larger vocabulary than either the Germanic languages or the members of the Romance language family to which French belongs.
• English also is ready to accommodate foreign words, and as it has become an international language, it has absorbed vocabulary from a large number of other sources.
• This does, of course, assume that one will ignore "agglutinative" languages; such as, Finnish, in which words can be stuck together in long strings of indefinite length, and which, therefore, have an almost infinite number of "words".