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Adjective used to describe a psychological event, usually specific though not exclusive to the brain itself, mentally "heard" by the individual experiencing it (as if everyone else on the planet can hear it too), but which in actuality of outward appearance goes entirely unheard, unnoticed, unsensed by others. The experience is often the result of having to hold back an inappropriate or violent audible expression, such as screaming, that would unquestionably make the individual feel better, but which if expressed would make the individual appear utterly insane. A key symptom that a silentomental event is happening is a compulsive and often repetitive visualization by the individual of him/herself engaging in that otherwise inappropriate act of audible expression.
During finals week a student may experience the silentomental screaming of his/her overworked, under-rested, hyper-caffeinated brain.

Adverbial usage:
Phobic of the dentist and given only a local anesthesia, Bob silentomentally endured his two-hour long root canal procedure.
by H. Parsons March 29, 2008