The Collaborative International Dictionary of English v.0.48:

Eagre \Ea"gre\, n. [AS. e['a]gor, ?gor, in comp., water, sea,
   e['a]gor-stre['a]m water stream, sea.]
   A wave, or two or three successive waves, of great height and
   violence, at flood tide moving up an estuary or river; --
   commonly called the bore or tidal bore. See Bore.
   Ealderman

WordNet (r) 3.0 (2006):

eagre
    n 1: a high wave (often dangerous) caused by tidal flow (as by
         colliding tidal currents or in a narrow estuary) [syn:
         tidal bore, bore, eagre, aegir, eager]