Source : Webster's Revised Unabridged Dictionary (1913)

Threepenny \Three"pen*ny\, a.
   Costing or worth three pence; hence, worth but little; poor;
   mean.

Source : WordNet®

threepenny
     adj 1: used of nail size; 1 1/8 in long
     2: of trifling worth [syn: {sixpenny}, {twopenny}, {tuppeny}, {two-a-penny},
         {twopenny-halfpenny}]