The words sex, sects sound the same but have different meanings and spellings. Why do sex, sects sound the same even though they are completely different words?
The answer is simple: sex, sects are homophones of the English language.
Plural form of sect.
The property or quality by which organisms are classified as female or male on the basis of their reproductive organs and functions.
Either of the two divisions, designated female and male, of this classification.
Females or males considered as a group.
The condition or character of being female or male; the physiological, functional, and psychological differences that distinguish the female and the male. See Usage Note at gender.
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.