Meaning
Last resort / Final card
Example
Penso em contar a verdade, será minha última cartada.
I'm thinking of telling the truth, it will be my last resort.
Origin
From card games — the last card you have left to play ('cartada'). Attested in Portuguese card-game vocabulary since the 19th century, then generalized to 'last resort.
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More idioms
Acertar na moscaTo guess correctly / To hit the nail on the headAmigo da onçaA fake/false friendAndar na linhaTo toe the line / To behave properlyArmar um barracoTo cause a public sceneRodar a baianaTo cause a public scene / To go ballisticArrumar sarna pra se coçarTo ask for troubleArrastar as asasTo hit on someone / To flirtAbrir o jogoTo come clean / To open upArregaçar as mangasTo roll up one's sleeves / To get to workAgarrar com unhas e dentesTo hold on for dear life / To seize an opportunity