The Collaborative International Dictionary of English v.0.48:

Tense \Tense\, a. [L. tensus, p. p. of tendere to stretch. See
   Tend to move, and cf. Toise.]
   Stretched tightly; strained to stiffness; rigid; not lax; as,
   a tense fiber.
   [1913 Webster]

         The temples were sunk, her forehead was tense, and a
         fatal paleness was upon her.             --Goldsmith.
   [1913 Webster] -- Tense"ly, adv. -- Tense"ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tensely
    adv 1: in a tense manner; "he sat down tensely"