Inflected Form(s): pu·ni·er; -est
Etymology: Anglo-French puisné younger, weakly, literally, born afterward, from puis afterward + né born
: slight or inferior in power, size, or importance : WEAK
1548, "inferior in rank," from M.Fr. puîné, from O.Fr. puisné "born later, younger" (12c., contrasted with aisné "first-born"), from puis "afterward" (from V.L. *postius, from L. postea, from post "after") + O.Fr. né "born," from L. natus, pp. of nasci "be born." Sense of "small, weak, insignificant" first recorded 1593. Online Etymology dictionary
Around here (Asheville, NC) puny is also used as a synonym for ill or sickly.