WordNet (r) 3.0 (2006):

underdeveloped
    adj 1: relating to societies in which capital needed to
           industrialize is in short supply [syn: developing,
           underdeveloped]
    2: not yet fully developed

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "underdeveloped":
   arrested, backward, behindhand, callow, coarse, crude, defective,
   deficient, embryonic, failing, hypoplastic, immature, in arrear,
   in arrears, in default, in embryo, in ovo, in short supply,
   in the rough, inadequate, incomplete, infant, lacking, missing,
   needing, oversimple, part, partial, patchy, reductionistic,
   reductive, rough, roughcast, roughhewn, rude, rudimental,
   rudimentary, scant, scanty, scrappy, short, shy, simplistic,
   sketchy, stunted, unblown, uncultivated, uncultured, uncut,
   undeveloped, unfashioned, unfinished, unformed, unhewn, unlabored,
   unlicked, unpolished, unprocessed, unprogressive, unrefined,
   untreated, unworked, unwrought, wanting