Lewis & Short

grōma or grūma, ae, f.

  1. I. A surveyor’s pole or measuring-rod, acc. to Paul. ex Fest. s. v. p. 72 Müll. and Non. 63, 6.
  2. II. Transf., the centre of a camp, where the measuring-rod was planted, so as to divide the camp into four quarters by streets meeting at that point, Hyg. de Limit. p. 164 Goes.