The words raining, reigning, reining sound the same but have different meanings and spellings. Why do raining, reigning, reining sound the same even though they are completely different words?
The answer is simple: raining, reigning, reining are homophones of the English language.
rain cats and dogs Informal To rain very heavily.
rain out To force the cancellation or postponement of (an outdoor event) because of rain. Used in passive constructions: The ball game was rained out.
To give abundantly; shower: rain gifts; rain curses upon their heads.
To send or pour down.
To be predominant or prevalent: Panic reigned as the fire spread.
To hold the title of monarch, but with limited authority.
To exercise sovereign power.
Dominance or widespread influence: the reign of reason.
tight rein Close control: kept expenses on a tight rein.
free To release from restraints; allow to go unchecked: gave rein to her emotions.
draw in the reins To slow down or stop by or as if by pressure on the reins.
To control a horse, for example, with reins.
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.