The words crews, cruise sound the same but have different meanings and spellings. Why do crews, cruise sound the same even though they are completely different words?
The answer is simple: crews, cruise are homophones of the English language.
Plural form of crew.
To sail or travel about, as for pleasure or reconnaissance.
To go or move along, especially in an unhurried or unconcerned fashion: "A whole cache of babies . . . cruised imperiously in their strollers, propelled by their mothers or by pairs of grandmothers” ( Anne Tyler).
To travel at a constant speed or at a speed providing maximum operating efficiency for a sustained period.
Informal To move leisurely about an area in the hope of discovering something: taxis cruising for fares.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License, 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.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").