The words clamber, clammer, clamor sound the same but have different meanings and spellings. Why do clamber, clammer, clamor sound the same even though they are completely different words?
The answer is simple: clamber, clammer, clamor are homophones of the English language.
To climb with difficulty, especially on all fours; scramble.
A difficult, awkward climb.
One who digs for clams.
A loud outcry; a hubbub.
A vehement expression of discontent or protest: a clamor in the press for pollution control.
A loud sustained noise. See Synonyms at noise.
To make a loud sustained noise or outcry.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition, from Wiktionary, Creative Commons Attribution/Share-Alike License and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").