There is no single sensible answer to this question. It's impossible to count the number of words in a language, because it's so hard to decide what actually 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 (e.g. 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 it might also be written as hot-dog or even hotdog?
這個問題并沒有一個簡單而合理的答案。想要計算一種語言里有多少單詞是不可能做到的，因為很難定義究竟什么才是一個單詞。Dog究竟算一個單詞還是兩個（名詞指一種動物，動詞指長期跟隨）？如果算作兩個，那么我們是否也要把它的變型也單獨計算（例如：復數(shù)名詞dogs，第三人稱單數(shù)現(xiàn)在時dogs）？Dog-tired（筋疲力盡）算一個單詞還是兩個連在一起的單詞？既然Hot dog（熱狗）可以被寫成hot-dog甚至hotdog，它真的算兩個單詞嗎？

It's 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? Teenage?slang? Abbreviations?
同樣，很難定義什么才算英語。醫(yī)學和科學名詞怎么辦？法律中使用的拉丁詞匯、烹飪中使用的法語詞匯、學術(shù)寫作中使用的德語詞匯和武術(shù)中使用的日語詞匯怎么辦？蘇格蘭方言算不算？青少年的俚語呢？縮寫呢？

The Second Edition of the 20-volume?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 rest is made up of?exclamations, conjunctions, prepositions, suffixes, etc. And these figures don't take account of entries with senses for different word classes (such as noun and adjective).
長達20卷的《牛津英語詞典》第二版中有171476個仍在使用的單詞詞條，還有47156個廢棄單詞詞條。此外還要加上約9500個派生詞作為詞條下面的分項。這些單詞中，超過半數(shù)是名詞，約四分之一的單詞是形容詞，七分之一左右的詞是動詞，剩下的是感嘆詞、連詞、介詞和詞綴等。這一數(shù)字并未把單詞的不同詞性（例如名詞和形容詞）分別計算。

易詞解詞（BY 摩西）

Oxford n. 牛津（英國城市）。要說“牛津”這兩個字的翻譯真是傳神，ox是牛，而ford是淺灘和動詞的涉水而過。牛津這地方本有一條小河，但水流不深，拉著牛車可以跋涉而過，故得名。有意思的是，這個ford是日耳曼詞源，同德國城市法蘭克福Frankfurt中的furt，F(xiàn)rankfurt，法蘭克人的渡口之意。與希臘拉丁詞源的port-詞根表港口、搬運同源，于是airport,import,export,portal這些就好理解了。

quarter n. 四分之一；地區(qū)；季度；一刻鐘；兩角五分；節(jié)。拉丁詞根quadr-,quart-表四分之一/第四，quart夸脫是四分之一加侖，quadruple是四倍的（ple-表fold倍數(shù)），quarantine檢疫；隔離，是歷史上歐洲黑死病期間進入威尼斯港口的船舶需要在港外停留40天觀察有沒有攜帶病菌，下次你要是看見某輛車的進氣柵處有QUATTRO的字樣，那它就是一輛四輪驅(qū)動的車。

This suggests that there are, at the very least, a quarter of a million distinct 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 three quarters of a million.
這表明，英語中有至少25萬單詞，其中的20%可能已經(jīng)不再使用。這25萬單詞中不包括變型、《牛津英語詞典》中不收錄的專業(yè)術(shù)語和地方方言、以及尚未被已出版詞典收錄的單詞。如果要把同一單詞的不同含義分別計算，英語單詞的總數(shù)可能會接近75萬。