The words basal, basil sound the same but have different meanings and spellings. Why do basal, basil sound the same even though they are completely different words?
The answer is simple: basal, basil are homophones of the English language.
Of, relating to, located at, or forming a base.
Botany Located at or near the base of a plant stem, or at the base of any other plant part: basal placentation.
Of primary importance; basic.
An Old World aromatic annual herb (Ocimum basilicum) in the mint family, cultivated for its leaves. Also called sweet basil.
The leaves of this plant used as a seasoning.
Any of various plants in the genus Ocimum, native to warm regions, having aromatic foliage and terminal clusters of small, usually white flowers.
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.