The Collaborative International Dictionary of English v.0.48:

Unfilled \Unfilled\
   See filled.

WordNet (r) 3.0 (2006):

unfilled
    adj 1: of purchase orders that have not been filled [ant:
           filled]

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "unfilled":
   abandoned, available, deserted, dog-hungry, empty, famished,
   famishing, fasting, forsaken, free, godforsaken, half-famished,
   half-starved, hungering, hungry, open, peckish,
   pinched with hunger, ravening, ravenous, sharp-set, starved,
   starving, tenantless, uninhabited, unmanned, unoccupied, unpeopled,
   unpopulated, unstaffed, untaken, untenanted, untended, vacant,
   voracious, wolfish