In chemistry, an arsenite is a chemical compound containing an arsenic oxoanion where arsenic has oxidation state +3. Note that in fields that commonly deal with groundwater chemistry, arsenite is used generically to identify soluble AsIII anions. IUPAC have recommended that arsenite compounds are to be named as arsenate(III), for example ortho-ar...
• (n.) A salt formed by the union of arsenious acid with a base.
Ar'sen·ite noun [ Confer French arsénite .] (Chemistry) A salt formed by the union of arsenious acid with a base. 
a salt or ester of arsenous acid.