The words leach, leech sound the same but have different meanings and spellings. Why do leach, leech sound the same even though they are completely different words?
The answer is simple: leach, leech are homophones of the English language.
To remove soluble or other constituents from by the action of a percolating liquid.
To empty; drain: "a world leached of pleasure, voided of meaning” ( Marilynne Robinson).
To be dissolved or passed out by a percolating liquid.
The act or process of leaching.
Any of various chiefly aquatic bloodsucking or carnivorous annelid worms of the class Hirudinea, of which one species (Hirudo medicinalis) was formerly used by physicians to bleed patients and is now sometimes used as a temporary aid to circulation during surgical reattachment of a body part.
One that preys on or clings to another; a parasite.
Archaic A physician.
To bleed with leeches.
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.