Lewis & Short

ag-grĕgo (adg-), āvi, ātum, 1, v. a. [grex, grego].

  1. * I. To bring or add to a flock: ADGREGARE: ad gregem ducere, Paul. ex Fest. p. 23 Müll.
    Hence,
  2. II. To add to something: se adgregare, to attach one’s self to, to follow or adhere to (more rare than adjungere, and only in prose, but class.): si secum suos eduxerit, et eodem ceteros naufragos adgregaverit, Cic. Cat. 1, 12: filium eodem indicio ad patris interitum, to implicate in, id. Vatin. 10, 25: te semper in nostrum numerum adgregare soleo, to add to, reckon among, id. Mur. 7, 16: meam voluntatem ad summi viri dignitatem adgregāssem, had shown my zeal for the increase of his reputation, id. Fam. 1, 9: se ad eorum amicitiam, to join or ally themselves to, Caes. B. G. 6, 12; Vell. 2, 91: oppidani adgregant se Amphotero, Curt. 4, 5; and instead of se adgregare, the pass.: ne desciscentibus adgregarentur, Suet. Ner. 43.