The words til, till sound the same but have different meanings and spellings. Why do til, till sound the same even though they are completely different words?
The answer is simple: til, till are homophones of the English language.
Until. See Usage Note at till2.
To prepare (land) for the raising of crops, as by plowing and harrowing; cultivate.
A drawer, small chest, or compartment for money, as in a store.
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.