The Collaborative International Dictionary of English v.0.48:
Illegible \Il*leg"i*ble\, a. Incapable of being read; not legible; as, illegible handwriting; an illegible inscription. -- Il*leg"i*ble*ness, n. -- Il*leg"i*bly, adv. [1913 Webster]WordNet (r) 3.0 (2006):
illegible adj 1: (of handwriting, print, etc.) not legible; "illegible handwriting" [ant: legible]