Webster’s Revised Unabridged Dictionary · 1913
Methionic
Meth′i·on′ic (mĕth′ī·ŏn′ĭk), 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.