noun
: any acid derived from boric oxide: as
a. : a white crystalline toxic weak acid H 3 BO 3 that occurs naturally in solution in the fumaroles of Tuscany, that is easily obtained from its salts, and that is used for many of the same purposes as borax and also in electroplating and formerly as a weak antiseptic (as in eyewashes) — called also boracic acid, orthoboric acid
b. : metaboric acid
c. : tetraboric acid