The Collaborative International Dictionary of English v.0.48:
Sedge \Sedge\, n. [OE. segge, AS. secg; akin to LG. segge; --
probably named from its bladelike appearance, and akin to L.
secare to cut, E. saw a cutting instrument; cf. Ir. seisg, W.
hesg. Cf. Hassock, Saw the instrument.]
1. (Bot.) Any plant of the genus Carex, perennial,
endogenous, innutritious herbs, often growing in dense
tufts in marshy places. They have triangular jointless
stems, a spiked inflorescence, and long grasslike leaves
which are usually rough on the margins and midrib. There
are several hundred species.
Note: The name is sometimes given to any other plant of the
order Cyperaceae, which includes Carex, Cyperus,
Scirpus, and many other genera of rushlike plants.
2. (Zool.) A flock of herons.
Sedge hen (Zool.), the clapper rail. See under 5th Rail.
Sedge warbler (Zool.), a small European singing bird
(Acrocephalus phragmitis). It often builds its nest
among reeds; -- called also sedge bird, sedge wren,
night warbler, and Scotch nightingale.