Lewis & Short

assectātĭo (ads-), ōnis, f. [assector].

  1. I. An (assiduous, respectful) attendance (as that of clients, etc.): in petitionibus opera atque adsectatio, Cic. Mur. 34: so Q. Cic. Petit. Cons. 9.
  2. II. Observation, study: magna caeli adsectatio, Plin. 2, 20, 18, § 82.