The species of fungus Tylopilus felleus.

(of an environment) Very cold and unpleasant.

Citrullus colocynthis, a vine that bears a hard, bitter fruit. / A bitter preparation applied to an object to discourage dogs from chewing on it.

plural of bitter orange

plural of bitter vetch

A plant with bitter, lentil-like seeds that are edible with special processing, but are now mostly fed to livestock, Vicia ervilia. / The heath pea (Lathyrus linifolius)

(figuratively) Something unpleasant that must be accepted or endured. / Used other than figuratively or idiomatically: see bitter pill, swallow.

plural of bitter pill to swallow

(idiomatic) To accept positive things with negative things.

(idiomatic) To accept or endure an unpleasant situation.