† hydro-ˈacidChem.Obs. = hydracid. 1845Todd & Bowman Phys.Anat. I. 5 Hydrogen would be [united] to a simple or compound radicle (chlorine or cyanogen), to form a hydro-acid.c1865G. Gore in Circ.Sc. I. 226/2 The hydro-acids—hydrochloric acid, for example.