Americans use "-ize/yze" endings where the British will use "-ise." Some examples include American spellings of "analyze, memorize, editorialize" compared to the British spellings of "analyse, memorise, editorialise." While Americans are strict about the use of "-ize," the British do allow a little more leeway. Officially they will accept either spelling, with the "-ize" being called the Oxford spelling. The "-ize" comes from Greek spellings while the "-ise" comes from Romance languages such as Latin and French.
Perhaps one of the best-known differences is the ending of "-or" in American English compared to the "-our" of British English. This shows up in words such as color/colour, honor/honour, neighbor/neighbour and rumor/rumour. The American "-or" ending occurs only when the final syllable is unstressed. When it is stressed, such as in troubadour or contour, the "-our" ending is retained. Noah Webster's American English dictionary is considered the source of the American difference in spelling.
French, Latin and Greek influences are the origin of the differences in British and American words ending in "-er" or "-re." Generally speaking, American words end in "-er" while their British counterparts end in "-re." In British spelling, it is the words of French, Latin or Greek origin that end in "-re" while words of other origins end in "-er," though there are numerous exceptions. Examples of words that are spelled differently include center/centre, liter/litre, caliber/calibre. Americans do occasionally borrow British spellings for such words as theatre and centre, though those should be used only if the official names of buildings use those spellings, while theater and center should be used in all other instances of American English.
Several words ending in "-ck" or "-k" in American English instead end in "-que" in British English. Examples of this include check/cheque, bank/banque.
Words that end in double consonants tend to keep their doubled consonant in British English when a suffix beginning with a vowel is added to words with a final stressed syllable. In all other cases, the doubled consonant is dropped. In American English, the spelling remains unchanged. Examples include willful/wilful, enrollment/enrolment, skillful/skilful.