formalto join with other people or groups in order to oppose an enemy:
U.S. officials expect other Western governments to make common cause with them over the arrests.
5 [countable]lawSCLa case that is brought to a court of law
➔ lost cause
at lost2 (12)WORD CHOICE: WORD CHOICE: cause, reasonA causeis something such as an action, event, or situation that makes something happen• The cause of the accident is not known.• a determination to tackle the causes of crimeA reasonis an explanation for something• Can you think of any reason why he would behave in this way? • There is a good reason (NOT a good cause) for my decision. GRAMMARUse the cause of, not 'cause for' or 'cause why'• What is the cause of all this unrest?!!cause for is used in some expressions such as cause for alarm/concern/complaint/optimism/satisfaction• There is no cause for concern. • His remarks give some cause for hope.Use cause somebody to do something, not 'cause that somebody does something'• A cat ran into the road, causing her to brake suddenly (NOT causing that she braked suddenly).
Definition from the Longman Dictionary of Contemporary English Advanced Learner's Dictionary.