Of uncertain affinity; deep or open sea, i.e. The main -- depth, sea.
a. properly, the sea i. e. the high sea, the deep (where ships sail; accordingly but a part of the sea, θάλασσα, Aristotle, Probl. sect. 23 quaest. 3 (p. 931{b}, 14f) ἐν τῷ λιμενι ὀλίγη ἐστιν ἡ θάλασσα, ἐν δέ τῷ πελάγει βαθεῖα. Hence) τό πέλαγος τῆς θαλάσσης,aequor maris (A. V. the depth of the sea; cf. Trench, § xiii.), Matthew 18:6 (so too Apollonius Rhodius, 2, 608; πέλαγος αἰγαιας ἁλός, Euripides, Tro. 88; Hesychius πέλαγος ... βυθός, πλάτος θαλάσσης. Cf. Winers Grammar, 611 (568); (Trench, as above)).
b. universally, the sea: τό πέλαγος τό κατά τήν Κιλικίαν, Acts 27:5 (see examples from Greek authors in Passow, under the word πέλαγος, 1; (Liddell and Scott, under I.)).