TONUS By N., Pam M.S. - April 29, 2013 noun. An ongoing, slight stretching, pulling, tension, or contracting in muscles whenever they are at rest. TONUS: "The tonus state of her muscles may have accounted for their increased size." Related Psychology Terms TORTICOLLIS TENSION HEADACHE TONIC LABYRINTH REFLEX TENSION TONIC REFLEX TRICHOTILLOMANIA ORGASM TENDON REFLEX PILOERECTION MUSCLE-CONTRACTION HEADACHE Cite this page: N., Pam M.S., "TONUS," in PsychologyDictionary.org, April 29, 2013, https://psychologydictionary.org/tonus/ (accessed November 15, 2019).