Lewis & Short

observātĭo, ōnis, f. [observo], a watching, observing, observance (class.).

  1. I. In gen.: observationi operam dare, Plaut. Mil. 2, 6, 5: siderum, Cic. Div. 1, 1, 2.
    As a gift or faculty, the power of observation, Plin. 18, 29, 69, § 284.
  2. II. In partic.
    1. A. An office, duty, service (eccl. Lat.): Dei sui et expiationis, Vulg. 2 Esdr. 12, 44: in observationibus sicut fas est, id. 1 Macc. 12, 11.
    2. B. An observation, remark; a precept, rule (post-Aug.), Plin. 17, 21, 35, § 163: dare observationes aliquas coquendi, id. 22, 23, 47, § 99: sermonis antiqui, Suet. Gram. 24.
    3. C. In partic., circumspection, care, exactness: summa erat observatio in bello movendo, Cic. Off. 1, 11, 36.
    4. D. Regard, respect, esteem, reverence (post-class.): religionibus suam observationem reddere, Val. Max. 1, 1, 8: Christianitatis, Cod. Th. 12, 1, 112: divina, ib. 12, 1, 104.
    5. E. Display, outward show (eccl. Lat.): non venit regnum Dei cum observatione, Vulg. Luc. 17, 20.
  3. F. Observance: dierum, Gell. 3, 2, 3.