The words shear, sheer sound the same but have different meanings and spellings. Why do shear, sheer sound the same even though they are completely different words?
The answer is simple: shear, sheer are homophones of the English language.
The act, process, or result of shearing.
To remove (fleece or hair) by cutting or clipping.
To remove the hair or fleece from.
To cut with or as if with shears: shearing a hedge.
To swerve or cause to swerve from a course.
A swerving or deviating course.
Nautical The upward curve or amount of upward curve of the longitudinal lines of a ship's hull as viewed from the side.
Nautical The position in which a ship at anchor is maintained in order to keep it clear of the anchor.
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").