imperceivable

From im- +‎ perceivable.

imperceivable (comparative more imperceivable, superlative most imperceivable)

1. that cannot be perceived; imperceptible
   • 1692–1717, Robert South, Twelve Sermons Preached upon Several Occasions, volume (please specify |volume=I to VI), London:

     by a long Train of gradual , imperceivable Encroaches of the Flesh upon the Spirit

• “imperceivable”, in Webster’s Revised Unabridged Dictionary, Springfield, Mass.: G. & C. Merriam, 1913, →OCLC.