1. (Science: botany) Any plant of the genus Carex, perennial, endogenous 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.
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. These are plants that look a bit like grasses, but they belong to a different plant family, the Cyperaceae.
most grasses have stems that are round in cross-section, while the stems of sedges are triangular in cross–section, thus you can remember the difference with the rhyme sedges have edges.
2. (Science: zoology) A flock of herons. Sedge ken, a small European singing bird (Acrocephalus phragmitis). It often builds its nest among reeds.
Synonym: sedge bird, sedge wren, night warbler, and Scotch nightingale.
Origin: 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.