Of, pertaining to, or derived from, chlorine; -- said of those compounds of chlorine in which this element has a valence of three, the next lower than in chloric compounds; as, chlorous acid, HClO2.  [1913 Webster]

 Pertaining to, or resembling, the electro-negative character of chlorine; hence, electro-negative; -- opposed to basylous or zincous.  [1913 Webster]