plural of black birch tree

(humorous, folklore) A fictional bird said to fly backwards or in circles.

Any of the species of the genus Sicista, found in Eurasian forests and steppes.

plural of birch mouse

Said or written to a person after his or her birthday in order to convey the good wishes of the speaker or writer.

Said or written to a deceased person on his or her birthday in order to convey the good wishes of the speaker or writer.

A birthday of a person after his or her death.

(probability theory) The counterintuitive observation that a random group of people needs to have only 23 members before there is a 50% chance of two of them having the same birthday.

Used other than figuratively or idiomatically: see canary, bird. / (slang) A jailbird. / (slang) A mistress.

plural of biradicaloid