The words od, odd sound the same but have different meanings and spellings. Why do od, odd sound the same even though they are completely different words?
The answer is simple: od, odd are homophones of the English language.
An alleged force or natural power, supposed, by Reichenbach and others, to produce the phenomena of mesmerism, and to be developed by various agencies, as by magnets, heat, light, chemical or vital action, etc.; — also called odyle or the odylic force.
Deviating from what is ordinary, usual, or expected; strange or peculiar: an odd name; odd behavior. See Synonyms at strange.
Being in excess of the indicated or approximate number, extent, or degree. Often used in combination: invited 30-odd guests.
Constituting a remainder: had some odd dollars left over.
Small in amount: jingled the odd change in my pockets.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License, from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.