The words band, banned sound the same but have different meanings and spellings. Why do band, banned sound the same even though they are completely different words?
The answer is simple: band, banned are homophones of the English language.
A thin strip of flexible material used to encircle and bind one object or to hold a number of objects together: a metal band around the bale of cotton.
A strip or stripe that contrasts with something else in color, texture, or material.
A narrow strip of fabric used to trim, finish, or reinforce articles of clothing.
Something that constrains or binds morally or legally: the bands of marriage and family.
Simple past tense and past participle of ban.
Forbidden; not allowed.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition, from Wiktionary, Creative Commons Attribution/Share-Alike License and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.