Lewis & Short

2. intrŏĭtus, ūs, m. [introeo], a going in or into, an entering, entrance (class.).

  1. I. Lit.: nocturnus introitus Zmyrnam quasi in hostium urbem, Cic. Phil. 11, 2, 5: militum, Caes. B. C. 1, 21: in urbem, id. Dom. 28: sol in Geminos introitum facit, enters, Col. 11, 2, 43: primo statim introitu, at his very first entrance, Tac. H. 1, 31: aliquem introitu prohibere, Cic. Caecin. 13: cujus in Graeciam, Just. 2, 11, 1: introitum alicujus rei pellere, to keep a thing from entering, Plin. 20, 9, 39, § 101.
    With in and abl. (rare): sol introitum in Cancro facit, Col. 11, 2, 49.
      1. 2. Esp., the mouth of a river, its entrance into another: Averni, Sil. 13, 398; also as the entrance to it from the sea (cf. B. infra): Indi, Plin. 12, 12, 25, § 41 al.
    1. B. Transf., a place of entrance, passage: ad omnes introitus, qua adiri poterat, Cic. Caecin. 8: omnes introitus erant praeclusi, Caes. B. G. 5, 9: clandestinus, Suet. Ner. 48: aures duros et quasi corneolos habere introitus, Cic. N. D. 2, 57: portus, Caes. B. C. 3, 39, 2; Cic. Verr. 2, 5, 31, § 80: aedis, Nep. Paus. 5, 3: ad ipsum introitum exspectare macelli, Juv. 11, 10.
      In the abl.: INTROITO, Inscr. Orell. 2103.
  2. II. Trop.
    1. A. An entering, entrance upon an office or into a society: certum aliquid pro introitu dare, Plin. Ep. 10, 113: sacerdotii, Suet. Claud. 9: militiam illam cum introitu comparari volo, i. e. entrancemoney, Dig. 32, 1, 102.
    2. B. A beginning, introduction, prelude (syn.: principium, exordium, prooemium): fabulae Clodianae, Cic. Att. 1, 18: defensionis, id. Cael. 2, 3: in introitu hujus operis, Plin. 6, 27, 31, § 141.