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Old English leccan "to moisten, water, wet, irrigate," (see leak). The word disappears, then re-emerges late 18c. in a technological sense in reference to percolating liquids. Related: Leached; leaching.
leaching leach·ing (lē'chĭng)
The removal of soluble material from a substance, such as soil or rock, through the percolation of water. Organic matter is typically removed from a soil horizon and soluble metals or salts from a rock by leaching. Leaching differs from eluviation in that it affects soluble, not suspended, material and often results in the complete removal of the material from the soil or rock.