The words coif, quaff sound the same but have different meanings and spellings. Why do coif, quaff sound the same even though they are completely different words?
The answer is simple: coif, quaff are homophones of the English language.
A tight-fitting cap worn under a veil, as by nuns.
A white skullcap formerly worn by English lawyers.
A heavy skullcap of steel or leather, formerly worn under a helmet or mail hood.
To drink (a beverage) heartily: quaffed the ale with gusto.
To drink a liquid heartily: quaffed from the spring.
A hearty draft of liquid.
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.