Real Dictionary

bittern in American English 1
any of a subfamily (Botaurinae) of wading birds, including a genus (Botaurus) noted for the resounding, thumping call of the male
noun: any of several tawny brown herons that inhabit reedy marshes, as Botaurus lentiginosus (American bittern), of North America, and B. stellaris, of Europe

bittern in American English 2
the bitter liquid left after the crystallization of salt from brine
noun: a bitter solution remaining in salt making after the salt has crystallized out of seawater or brine, used as a source of bromides, iodides, and certain other salts

bittern in British English 1
noun: any wading bird of the genera Ixobrychus and Botaurus, related and similar to the herons but with shorter legs and neck, a stouter body, and a booming call: family Ardeidae, order Ciconiiformes

bittern in British English 2
noun: the bitter liquid remaining after common salt has been crystallized out of sea water: a source of magnesium, bromine, and iodine compounds