The words forbear, forebear sound the same but have different meanings and spellings. Why do forbear, forebear sound the same even though they are completely different words?
The answer is simple: forbear, forebear are homophones of the English language.
To refrain from; resist: forbear replying. See Synonyms at refrain1.
To desist from; cease.
Obsolete To avoid or shun.
To hold back; refrain.
A person from whom one is descended; an ancestor. See Synonyms at ancestor.
Definitions 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").