The words basest, bassist sound the same but have different meanings and spellings. Why do basest, bassist sound the same even though they are completely different words?
The answer is simple: basest, bassist are homophones of the English language.
superlative form of base: most base.
A musician who plays a bass instrument, especially a double bass or bass guitar.
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.
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").