Source : Webster's Revised Unabridged Dictionary (1913)

Methionic \Meth`i*on"ic\, a. [Methyl + thionic.] (Chem.)
   Of, pertaining to, or designating, a sulphonic (thionic) acid
   derivative of methane, obtained as a stable white crystalline
   substance, {CH2.(SO3H)2}, which forms well defined salts.