Answer:
% English dictionary, words common to American and British
% spelling; must add one out of each of the pairs
% colour/color.dic
% labelled/labeled.dic
% centre/center.dic
% ize/ise.dic
% Extracted from US.dic and UK.dic, but with the 2 and 3 letter words
% of US.dic only.
% Patrick W. Daly 1998/05/19
% Update: 2000/03/02
% remove -yze and -yse words to yse.dic and yze.dic
% move advertise to here (is never advertize)
Explanation: