(a.) Not perceivable by the eye; invisible; unseen.

DR alive to appreciative of apprised of awake to aware of back to back backstage before an audience before the footlights behind behind the curtain behind the veil camouflaged causal causative cognizant of concealed conscious of constitutive covertly decisive determinative disguised down left down right downstage effectual etiological formative hep to hidden imperceptible in a corner in a whisper in back of in darkness in hidlings in secret in the background in the dark in the know in the limelight in the rear in the secret indiscernible informed of insensible institutive invisible latent let into mindful of no stranger to nobody the wiser occasional off stage on the stage on to onstage originative out of sight pivotal privy to secret secretly seized of sensible of sensible to sightless sotto voce streetwise sub rosa submerged tandem unapparent unbeheld unbeholdable undeceived under the breath under the rose undercover underground undiscernible unnoticed unobserved unperceivable unperceived unrealized unseeable unseen unviewed unwitnessed up left upright upstage viewless wise to with bated breath