The words tear, tier sound the same but have different meanings and spellings. Why do tear, tier sound the same even though they are completely different words?
The answer is simple: tear, tier are homophones of the English language.
A great rush; a hurry.
To pull apart or into pieces by force; rend.
To make (an opening) by ripping: tore a hole in my stocking.
To lacerate (the skin, for example).
One of a series of rows placed one above another: a stadium with four tiers of seats.
A rank or class.
To arrange (something) into or rise in tiers: tier a wedding cake; balconies that tier upward.
One that ties: a tier of knots.
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.