The Collaborative International Dictionary of English v.0.48:
Threepenny \Three"pen*ny\, a. Costing or worth three pence; hence, worth but little; poor; mean. [1913 Webster]WordNet (r) 3.0 (2006):
threepenny adj 1: used of nail size; 1 1/8 in long 2: of trifling worth [syn: sixpenny, threepenny, twopenny, tuppeny, two-a-penny, twopenny-halfpenny]