The words aurally, orally sound the same but have different meanings and spellings. Why do aurally, orally sound the same even though they are completely different words?
The answer is simple: aurally, orally are homophones of the English language.
By means of the ear or of audition; in an auditory manner.
Pertaining to <xref>sound</xref> or the <xref>ear</xref>.
with regard to sound or the ear
In an oral manner; by word of mouth; in words, without writing; vocally; verbally: as, traditions derived <em>orally</em> from ancestors.
By means of the mouth; through, in, or into the mouth.
Toward or in the mouth or oral region.
In an oral manner.
Definitions from The Century Dictionary., from Wiktionary, Creative Commons Attribution/Share-Alike License., from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved., from the GNU version of the Collaborative International Dictionary of English. and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.