The Collaborative International Dictionary of English v.0.48:
Incognoscible \In`cog*nos"ci*ble\, a. Incognizable. -- In`cog*nos"ci*bil"i*ty, n. IncoherenceWordNet (r) 3.0 (2006):
incognoscible adj 1: incapable of being perceived or known [syn: incognizable, incognoscible]