from
The Collaborative International Dictionary of English v.0.48
Subliminal \Sub*lim"i*nal\, 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.
Note: The existence of such an effect is still not
universally accepted.
[PJC]