noun
: either of two crystalline or powdery substances that are compounds of sodium metaborate with hydrogen peroxide and are used chiefly as bleaching agents and oxidizing agents and in mouthwashes and dentifrices:
a. or sodium perborate tetrahydrate : the compound NaBO 3 .4H 2 O or NaBO 2 .H 2 O 2 .3H 2 O made by reaction of sodium peroxide with a solution of borax or by electrolysis of a solution of borax and sodium carbonate
b. or sodium perborate monohydrate : the compound NaBO 3 .H 2 O or NaBO 2 .H 2 O 2 made by dehydration of the tetrahydrate