(idiomatic) A very important person, especially the highest-ranking individual in an organization. / (idiomatic) Some item of high value, especially a top prize or reward.

(entertainment, idiomatic) A breakthrough, especially the first big hit of a previously unknown performer or performers in the entertainment industry.

(informal) The Mississippi River. / (informal) The Missouri River.

A nickname for New York City.

(astronomy) The cosmic event that marks the beginning of time and the rapid expansion of space for the visible universe. The evolution of the universe since that beginning point is described by the Big Bang Theory.

(idiomatic) A person with a reputation of importance or power. / (idiomatic) A rare and significant chance to achieve fame or success.

(slang) Prison, jail. / (slang, obsolete) The workhouse. / A religious building of the Delaware Indians, representing the cosmos. / Used other than figuratively or idiomatically: see big, house.

(slang, street name) The drug heroin.

(US, slang) San Quentin prison.

(mathematical analysis) Upper bound function; see big O notation. / (slang, usually preceded by "the") Orgasm.