The words serf, surf sound the same but have different meanings and spellings. Why do serf, surf sound the same even though they are completely different words?
The answer is simple: serf, surf are homophones of the English language.
A member of the lowest feudal class, attached to the land owned by a lord and required to perform labor in return for certain legal or customary rights.
An agricultural laborer under various similar systems, especially in 18th- and 19th-century Russia and eastern Europe.
A person in bondage or servitude.
The waves of the sea as they break upon a shore or reef.
To engage in surfing.
Informal To look at a variety of things casually, especially while browsing the Internet or television channels.
To ride on or along (a wave) on a surfboard.
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.