Cat"i*on (?), n. [Gr. &?; downward + &?; going, p. pr. of &?; to go.] (Chem.) An electro-positive substance, which in electro-decomposition is evolved at the cathode; -- opposed to anion. Faraday.

• a positively charged ion
  
• the ion in an electrolyzed solution that migrates to the cathode