From The Collaborative International Dictionary of English v.0.48:
Bittern \Bit"tern\, n. [From Bitter, a.]
1. The brine which remains in salt works after the salt is
concreted, having a bitter taste from the chloride of
magnesium which it contains.
[1913 Webster]
2. A very bitter compound of quassia, cocculus Indicus, etc.,
used by fraudulent brewers in adulterating beer. --Cooley.
[1913 Webster]
From The Collaborative International Dictionary of English v.0.48:
Bittern \Bit"tern\, n. [OE. bitoure, betore, bitter, fr. F.
butor; of unknown origin.] (Zool.)
A wading bird of the genus Botaurus, allied to the herons,
of various species.
[1913 Webster]
Note: The common European bittern is Botaurus stellaris. It
makes, during the brooding season, a noise called by
Dryden bumping, and by Goldsmith booming. The American
bittern is Botaurus lentiginosus, and is also called
stake-driver and meadow hen. See Stake-driver.
[1913 Webster]
Note: The name is applied to other related birds, as the
least bittern (Ardetta exilis), and the sun
bittern.
[1913 Webster]