Lewis & Short

sĕnācŭlum, i, n. [senatus].

  1. I. Orig., an open place on the Forum, near the Grœcostasis, serving for the meetings of the Senate: senaculum supra Graecostasim, ubi aedis Concordiae et basilica Opimia. Senaculum vocatum, ubi senatus aut ubi seniores consisterent, dictum ut gerusia apud Graecos, Varr. L. L. 5, § 156 Müll.; so Val. Max. 2, 2, 6; Liv. 41, 27, 7.
  2. II. Later, in gen., for any council-hall of the Senate (including the curiae): senacula tria fuisse Romae, in quibus senatus haberi solitus sit, memoriae prodidit Nicostratus, etc., Fest. p. 347 Müll.; so Lampr. Elag. 4; Vop. Aurel. 49; cf. Becker, Antiq. 1, p. 286.