The Collaborative International Dictionary of English v.0.48:
Indiscernible \In`dis*cern"i*ble\, a. [Pref. in- not + discernible: cf. F. indiscernable.] Not to be discerned; imperceptible; not discoverable or visible. [1913 Webster] Secret and indiscernible ways. --Jer. Taylor. -- In`dis*cern"i*ble*ness, n. -- In`dis*cern"i*bly, adv. Indiscerpibility