- any of several tawny brown herons that inhabit reedy marshes, as Botaurus lentiginosus(American bittern ), of North America, and B. stellaris, of Europe.
- any of several small herons of the genus Ixobrychus, as I. exilis(least bittern ), of temperate and tropical North and South America.
- 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.
- 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
- the bitter liquid remaining after common salt has been crystallized out of sea water: a source of magnesium, bromine, and iodine compounds
