The words cerate, serrate sound the same but have different meanings and spellings. Why do cerate, serrate sound the same even though they are completely different words?
The answer is simple: cerate, serrate are homophones of the English language.
A hard, unctuous, fat- or wax-based solid, sometimes medicated, formerly applied to the skin directly or on dressings.
Having or forming a row of small sharp projections resembling the teeth of a saw: serrate teeth; a serrate talon.
Having a saw-toothed edge or margin notched with toothlike projections: serrate leaves.
To make serrate or saw-toothed; jag the edge of.
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").