Meaning
To try to hide the obvious / To bury one's head in the sand
Example
Não adianta tapar o sol com a peneira, todo mundo já sabe que a empresa está falindo.
There's no point hiding the obvious, everyone already knows the company is going bankrupt.
Origin
A 'peneira' is a sieve — trying to cover the sun with it is comically futile. The phrase is Portuguese (Portugal and Brazil) and dates to at least the 19th century.
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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