(usually with the) the ocean, the open sea; also in plural.

A way over the sea; the sea as a means of communication; the open sea. Also (nonce-use) a channel made for the sea.

the deep. The deep sea, the ocean, the main. poetic and rhetorical (without plural.)

The great abyss of waters; the deep, n. Obsolete.

Usually with the. The vast continuous body of salt water covering the greater part of the earth's… Independently of sea.

Chiefly literary and poetic. The middle of the sea, the open sea. Obsolete.

Chiefly poetic. The deepest or innermost part of something; a very deep place; an abyss; spec. the depths of the sea (cf. deep, n. 3a). Also figur…

The high sea; = main, n.1 5a. Also figurative.

In plural in same sense.

Short for main sea, n.; the open sea. Now chiefly poetic.

(a) high water; (b) a large or full-flowing body of water; (c) = main sea, n.

the deep. Formerly also in plural in same sense. Obsolete.

The deeper part of the sea or ocean at a distance from the shore. Used attributively or as adj.: Of or belonging to the deep sea.

Variant of deep sea, n. (apparently associated with dip), esp. in dipsy-lead, dipsy-line.

The middle of an ocean. Frequently in in mid-ocean.

Originally Nautical. The open sea. Chiefly in in blue water: on or in the open sea.

In Shetland and Orkney: The deep or main sea: now used only in connection with deep-sea fishing; hence, the part of the deep-sea frequented by…

In western Canada and north-western U.S.: the sea, the ocean.

Anything that is wide, sometimes contrasted with a corresponding thing that is narrow; esp. a wide or open space or region.