1 (usually Grand Slam) ( trademark in the UK) a set of major championships or matches in a particular sport in the same year, in particular tennis, golf, or rugby union:the tennis Grand Slam consists of the four most difficult major tournaments on the international circuit
any of the individual championships that comprise a Grand Slam:the season’s final Grand Slam at Flushing Meadows
the winning of all the individual championships that comprise a Grand Slam:the Springboks' dreams of a first Grand Slam since 1961 were ended by defeats against Ireland and England
2 Bridge the bidding and winning of all thirteen tricks.
3 Baseball a home run hit when each of the three bases is occupied by a runner, thus scoring four runs.
early 19th century (as a term in cards, especially bridge): from slam2
grand slam in other Oxford dictionaries
Definition of grand slam in the US English dictionary