underthreshold
Positioned below a threshold.
Being below the threshold or outside of the ordinary limits of consciousness; subconscious; subliminal.
The notion "underthreshold" is to be explained as all that which is under the ordinary threshold or outside the customary bounds of consciousness; [...]
Where it comes from
From under- + threshold, probably a calque of German unterschwellig (“subliminal”, literally “under-threshold”), from unter- (“under-”) + Schwelle (“threshold”). More at under, sill.
Adapted from the Wiktionary entry underthreshold (CC BY-SA 4.0).