The words based, baste sound the same but have different meanings and spellings. Why do based, baste sound the same even though they are completely different words?
The answer is simple: based, baste are homophones of the English language.
founded on; having a basis; often used in combining forms
Simple past tense and past participle of base.
Being derived from (usually followed by on or upon).
Having a base
To sew loosely with large running stitches so as to hold together temporarily.
To moisten (meat, for example) periodically with a liquid, such as melted butter or a sauce, especially while cooking.
To beat vigorously; thrash. See Synonyms at beat.
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").