Lewis & Short

aestŭārĭum, i, n. [aestus].

  1. I. A part of the sea-coast which, during the flood-tide, is overflowed, but at the ebb-tide is left covered with mud or slime, a marsh, ἀνάχυσις: aestuaria sunt omnia, quā mare vicissim tum accedit, tum recedit, Gloss. ap. Fest. p. 380 Müll.: pedestria esse itinera concisa aestuariis, Caes. B. G. 3, 9: adfunditur autem aestuarium e mari flexuoso meatu, Plin. 5, 1, 1, § 3; Plin. Ep. 9, 23.
    Also,
  2. II. A channel extending inland from the sea, and only filled with water at floodtide, a creek, inlet, Varr. R. R. 3, 17: in aestuaria ac paludes, Caes. B. G. 2, 28 Herz.; Tac. A. 2, 8; cf. id. Agr. 22.
  3. III. In mining t. t., an air-hole, air-shaft: secundum puteum dextra ac sinistra fodiunt aestuaria, Plin. 31, 3, 28, § 49; cf. Vitr. 8, 7; Pall. 9, 9.