Humor and humour are different spellings of the same word. Humor is preferred in American English, and humour is preferred in all other major varieties of English. The distinction extends to derivative participles, including humored/humoured and humoring/humouring. But in all varieties of English, the adjective humorous has no u in the second syllable.
Examples
For example, these American publications prefer humor, without the u:
This is not to say that first-rate humor can’t be squeezed out of the spy game. [Washington Post]
But the level of humor—much of it distinctly of the bathroom variety—is aimed squarely at the under-13 set. [USA Today]
Alà¿s’s work is full of these humorous touches, which convert potentially cold conceptual pranks into warm, whimsical human experiences. [Boston Globe]
And non-U.S. publications include the u in humour—for example:
With Ross’s keen editorial observations, his self-deprecating humour and his supporting cast of characters, Eyes is a welcome addition to my shelves of newspaper noir. [Calgary Herald]
It’s all very good humoured, in a British way, however much people worry that the civic character of the town is being eroded. [Telegraph]
In all varieties of English, there is no u in humorous and humorousness—for example:
Hundreds of comments have also been left on the auction, ranging from humorous puns and questions to praise for Johnson’s initiative. [Stuff.co.nz]
The second play, Greek is a humorous twist on the Oedipus legend reflected in 1980s London culture. [BBC News]
