before vowels hydr-, word-forming element in compounds of Greek origin, meaning "water," from Greek hydro-, combining form of hydor "water" (from suffixed form of PIE root *wed- (1) "water; wet"). Also sometimes a combining form of hydrogen.
"compound of oxygen with another element," 1790, from French oxide (1787), coined by French chemists Louis-Bernard Guyton de Morveau and Antoine Lavoisier from ox(ygène) (see oxygen) + (ac)ide "acid" (see acid (n.)).
<a href="https://www.etymonline.com/word/hydroxide">Etymology of hydroxide by etymonline</a>
Harper, D. (n.d.). Etymology of hydroxide. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/hydroxide