[1925–30; hydro-1 + sere2]This word is first recorded in the period 1925–30. Other words that entered Englishat around the same time include: Nazi, dropout, gimmick, hot spot, runouthydro- is a combining form meaning “water,” used in the formation of compound words. Otherwords that use the affix hydro- include: hydrofoil, hydrofracturing, hydroplane, hydrostat, hydrotherapy