To etiolate is to make something, especially a plant, become pale and weak. A lack of sunshine in your back yard might etiolate the roses you planted there.
You can use etiolate to describe what your uncle does to his house plants when he keeps his curtains closed for weeks — causing them to grow long, pale stems and tiny leaves from lack of sunlight. It's more common to find etiolate and the noun etiolation in science textbooks or botanists' studies. Etiolate comes from the French word étioler, "to blanch," and experts speculate that it may literally mean "to become like straw," from the French Norman étule, "a straw."