Lewis & Short

porrectĭo, ōnis, f. [1. porrigo],

  1. I. a stretching out, extending, extension: digitorum (opp. contractio), Cic. N. D. 2, 60, 150: bracchii, Auct. Her. 3, 15, 27.
  2. II. Concr., a straight line (opp. circinatio), Vitr. 10, 3, 8.