The words shire, shyer sound the same but have different meanings and spellings. Why do shire, shyer sound the same even though they are completely different words?
The answer is simple: shire, shyer are homophones of the English language.
a former administrative district of England; equivalent to a county
British breed of large heavy draft horse
A <xref>shire horse</xref>
A <xref>rural</xref> or outer <xref>suburban</xref> local government area of <xref>Australia</xref>.
<xref>comparative</xref> form of <xref>shy</xref>: more <xref>shy</xref>
A thrower; in <em>cricket</em>, one who, in the guise of bowling, throws the ball.
Definitions from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved., from Wiktionary, Creative Commons Attribution/Share-Alike License., from The Century Dictionary. and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.