%subliminal%

a. [ Pref. sub- + L. limen threshold. ] 1. (Philos.) Existing in the mind, but below the surface or threshold of consciousness; that is, existing as feeling rather than as clear ideas. [ Webster 1913 Suppl. ]

2. having or using an intensity of sensory stimulus insufficient to be perceived consciously, but having an effect on unconscious mental processes; as, subliminal advertising. The existence of such an effect is still not universally accepted. [ PJC ]