noun
: either of two poisonous crystalline salts usually made by reaction of hydrofluoric acid with soda ash:
a. : the normal salt NaF that is used in trace amounts in the fluoridation of water, in metallurgy, as a flux, as an antiseptic, and as an exterminator
b. or sodium bifluoride : the corrosive acid fluoride NaHF 2 used as a laundry sour, as a preservative especially for biological specimens, and in tinning steel; sodium hydrogen fluoride