Whitfield Diffie (private communication) concatenated all the files in the LISP directory of Gnu Emacs 21.1.1, removed comments (mostly), replaced everything except letters (a-z, A-Z), numerals (0-9), and hyphens, underscore, and colon, by carriage returns; finally ran sort | uniq -c | sort -nr. Here are the words with counts>5000: 48739 nil 45024 setq 43767 if 36920 t 29249 1 28873 \ 28675 defun 26355 \\ 25941 and 25566 let 23723 the 20944 0 18370 or 17903 a 16801 B 16742 car 16071 not 14338 to 14150 list 13659 point 13405 eq 12234 cdr 11970 s 11274 is 11260 nth 10981 2 10976 when 10630 defvar 10593 of 9652 define-key 9646 file 9571 interactive 9421 while 9026 - 9009 goto-char 8985 8711 in 8646 optional 8121 for 7848 string 7788 :group 7458 x 7388 arg 7310 concat 7205 cons 6882 quote 6855 progn 6738 buffer 6615 insert 6523 save-excursion 6234 end 6164 :type 6035 error 5935 cond 5919 defcustom 5831 name 5793 message 5378 3 5345 autoload 5261 n 5248 \n 5063 format