Well, this is my guess since there are cases of people being paid to maintain silence over a certain matter and in English we do talk about 'breaking silence' over an issue. Therefore I suppose that to pay someone for their silence is also another option to the one which my colleague has mentioned above

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"cala-a-boca" => hush money

Bribery - Wikipedia, the free encyclopedia
"Hush money" redirects here. For other uses, see Hush money (disambiguation). Bribery, a form of pecuniary corruption, is an act usually implying money or ...
www.en.wikipedia.org/wiki/Bribery

Ben Bernanke’s Hush Money by Gary North
26 Jul 2008 ... The $4 billion that the FDIC will pay to a handful of depositors at IndyMac is hush money. It is paid to them to silence every other ...
www.lewrockwell.com/north/north642.html

Edwards chair denies hush money - First Read - msnbc.com
8 Aug 2008 ... Hush money? "Of course it wasn't hush money!" .... So what's the game plan if campaign cash really was used as hush money for these two? ...
www.firstread.msnbc.msn.com/archive/2008/08/08/1257224.aspx -


A Dictionary of the Portuguese and English Languages, in Two ... - Google Books Result
by Antonio Vieyra, J P Aillaud - 1813 - Portuguese language
Cala a boca, hold your tongue, hush, or mum for that. Cum л боса aberta, a gape, staringly, with open mouth, as happens in vulgar admiration, ...
www.books.google.com.br/books?id=pTtBAAAAMAAJ...

An option.