Lewis & Short

intensĭo, ōnis, f. [intendo].

  1. I. A stretching out, straining, effort: oculorum, Scrib. Comp. 255.
    1. B. An intensifying, increase: calorem suum (sol) intensionibus ac remissionibus temperando fovet, Sen. Q. N. 7, 1, 3.
  2. II. The tune: gravis, media, acuta, Censor. 12.