Lewis & Short

nŭmĕrōsĭtas, ātis, f. [numerosus].

  1. I. A great number, multitude (post-class.): numerositas innumera, Macr. S. 5, 20: filiarum, Tert. Monog. 4: curialium, Cod. Th. 12, 5, 3: Scriptorum, Sid. Carm. 23, 150.
  2. II. Rhythm, harmony, Aug. Doctr. Christ. 4, 20; id. ib. 55, 109.