1.Generating electricity by conversion of the energy of running water. 2.Of, relating to, or using electricity so generated. hy′dro·e·lec′tri·cal·lyadv. hy′dro·e·lec·tric′i·ty(-ĭ-lĕk-trĭs′ĭ-tē)n. American Heritage® Dictionary of the English Language, Fifth Edi...