The words gel, jell sound the same but have different meanings and spellings. Why do gel, jell sound the same even though they are completely different words?
The answer is simple: gel, jell are homophones of the English language.
A colloid in which the disperse phase has combined with the dispersion medium to produce a semisolid material, such as a jelly.
See gelatin.
A jellylike substance used in styling hair.
To become a gel.
To become firm or gelatinous; congeal. See Synonyms at coagulate.
To take shape or fall into place; crystallize: A plan of action finally jelled in my mind.
To cause to become firm or gelatinous.
To cause to take shape; make clear and definite; crystallize.
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.
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").