The words waiting, weighting sound the same but have different meanings and spellings. Why do waiting, weighting sound the same even though they are completely different words?
The answer is simple: waiting, weighting are homophones of the English language.
The act of remaining inactive or stationary.
A period of time spent waiting.
in waiting In attendance, especially at a royal court.
A measure of the heaviness of an object.
The force with which a body is attracted to Earth or another celestial body, equal to the product of the object's mass and the acceleration of gravity.
A unit measure of gravitational force: a table of weights and measures.
A system of such measures: avoirdupois weight; troy weight.
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.