'Barrier reef' definitions:

Definition of 'barrier reef'

noun

A long coral reef near and parallel to the shore

From: GCIDE

Barrier \Bar"ri*er\, n. [OE. barrere, barere, F. barri[`e]re, fr. barre bar. See Bar, n.]
1. (Fort.) A carpentry obstruction, stockade, or other obstacle made in a passage in order to stop an enemy. [1913 Webster]
2. A fortress or fortified town, on the frontier of a country, commanding an avenue of approach. [1913 Webster]
3. pl. A fence or railing to mark the limits of a place, or to keep back a crowd. [1913 Webster]
No sooner were the barriers opened, than he paced into the lists. --Sir W. Scott. [1913 Webster]
4. Any obstruction; anything which hinders approach or attack. "Constitutional barriers." --Hopkinson. [1913 Webster]
5. Any limit or boundary; a line of separation. [1913 Webster]
'Twixt that [instinct] and reason, what a nice barrier! --Pope. [1913 Webster]
Barrier gate, a heavy gate to close the opening through a barrier.
Barrier reef, a form of coral reef which runs in the general direction of the shore, and incloses a lagoon channel more or less extensive.
To fight at barriers, to fight with a barrier between, as a martial exercise. [Obs.] [1913 Webster]