Hydroelectric; relating to power generated from moving water.

• Used attributively, as in hydro dam or hydro plant.

Hydroelectric power; electricity generated from water.

• By extension, a power utility or an electricity bill, chiefly Canada.

Hydroponic; grown without soil in nutrient solution.

A spa or hydropathic resort.

Abbreviation for hydrodynamics, the mechanics of fluids in motion.