How many words are there in English?

How many words are there in English?

http://www.oxforddictionaries.com/us/words/the-oec-facts-about-the-language

Like all natural languages, English consists of a small number of very common words, a larger number of intermediate ones, and then an indefinitely long 'tail' of very rare terms.

Vocabulary size (no. lemmas)	% of content in OEC	Example lemmas
10	25%	the, of, and, to, that, have
100	50%	from, because, go, me, our, well, way
1000	75%	girl, win, decide, huge, difficult, series
7000	90%	tackle, peak, crude, purely, dude, modest
50,000	95%	saboteur, autocracy, calyx, conformist
>1,000,000	99%	laggardly, endobenthic, pomological

...

What is the commonest word?

Based on the evidence of the Oxford English Corpus, which currently contains over 2 billion words, the 100 commonest English words found in writing around the world are as follows:

1     the 2     be 3     to 4     of 5     and 6     a 7     in 8     that 9     have 10    I 11    it 12    for 13    not 14    on 15    with 16    he 17    as 18    you 19    do 20    at 21    this 22    but 23    his 24    by 25    from

26    they 27    we 28    say 29    her 30    she 31    or 32    an 33    will 34    my 35    one 36    all 37    would 38    there 39    their 40    what 41    so 42    up 43    out 44    if 45    about 46    who 47    get 48    which 49    go 50    me

51    when 52    make 53    can 54    like 55    time 56    no 57    just 58    him 59    know 60    take 61    people 62    into 63    year 64    your 65    good 66    some 67    could 68    them 69    see 70    other 71    than 72    then 73    now 74    look 75    only

76    come 77    its 78    over 79    think 80    also 81    back 82    after 83    use 84    two 85    how 86    our 87    work 88    first 89    well 90    way 91    even 92    new 93    want 94    because 95    any 96    these 97    give 98    day 99    most 100   us

...

It's noticeable that many of the most frequently used words are short ones whose main purpose is to join other, longer words rather than determine the meaning of a sentence. These are known as 'function words'. 

It could be said that it's more interesting to explore the frequency of 'content words', as shown in the list below:

Nouns	Verbs	Adjectives
1       time 2       person 3       year 4       way 5       day 6       thing 7       man 8       world 9       life 10      hand 11      part 12      child 13      eye 14      woman 15      place 16      work 17      week 18      case 19      point 20      government 21      company 22      number 23      group 24      problem 25      fact	1       be 2       have 3       do 4       say 5       get 6       make 7       go 8       know 9       take 10      see 11      come 12      think 13      look 14      want 15      give 16      use 17      find 18      tell 19      ask 20      work 21      seem 22      feel 23      try 24      leave 25      call	1       good 2       new 3       first 4       last 5       long 6       great 7       little 8       own 9       other 10      old 11      right 12      big 13      high 14      different 15      small 16      large 17      next 18      early 19      young 20      important 21      few 22      public 23      bad 24      same 25      able

http://www.oxforddictionaries.com/top1000/english
http://www.oxforddictionaries.com/top1000/american_english

6,000 most frequently used English words
http://www.insightin.com/esl/