Lewis & Short

ārŭla, ae, f. dim. [ara].

  1. I. A small altar: ante hosce deos erant arulae, * Cic. Verr. 2, 4, 3; Vulg. Jer. 36, 22; 36, 23 bis; Jus Papir. in Macr. S. 3, 11; Arn. 3, p. 114; Inscr. Orell. 1630.—††
  2. II. Perh. the base of an altar (eccl. Lat.): quos (anulos) pones subter arulam altaris, Vulg. Exod. 27, 5; 38, 4.
  3. III. Among the Campanians, the turf laid altar-like round an elm-tree, Plin. 17, 11, 15, § 77.