One of the most noticeable differences between U.S. and British spelling is that of pairs like honor, honour and glamor, glamour.
The dropping of the u in such words is often attributed to the progressive thinking of American lexicographer Noah Webster (1758-1843), but Benjamin Franklin (1706-1790) thought of it first.
As a printer, Franklin had a professional interest in spelling. In 1768, he published his ideas and ordered a custom type font that included eight extra symbols. Years later, he approached Noah Webster with his innovations. Webster was not interested:
There seems to be an inclination in some writers to alter the spelling of words, by expunging the superfluous letters. This appears to arise from the same pedantic fondness for singularity that prompts new fashions of pronunciation. Thus they write the words favour, honour, etc. without u…”
In 1768, Webster’s view was that it was better “to speak our language with propriety and elegance as we have it,” but by 1789, he’d changed his mind:
I once believed that a reformation of our orthography would be unnecessary and impracticable. This opinion was hasty…I now believe with Dr. Franklin that such a reformation is practicable and highly necessary.”
By the time Webster published his first small dictionary in 1806, he was ready to drop the u from the “honour family” of nouns.
Modern British spelling retains the u in armour, behaviour, clamour, colour, endeavour, favour, fervour, flavour, glamour, harbour, humour, labour, neighbour, odour, rancour, rigour, rumour, saviour, splendour, and similar words.
Even in British spelling, however, when certain endings are added to these nouns, our becomes or.
The endings that alter the our spelling are -ous, -ary, -ation, -ial, and –ific. The following are both British and U.S. spellings: glamorous, humorous, laborious, rancorous, rigorous, coloration, honorary, honorific, armorial.
Note: the word behaviour seems to be putting up a fight. The OED gives both spellings, behavioural and behavioral.