Whitewash - definition
NOUN /ˈwaɪtˌwɒʃ/ [SINGULAR/UNCOUNTABLE] an attempt to stop people discovering the true facts about something, in order to prevent someone in authority from being criticized.
The first known use of the term is from 1591 in England.
Whitewash is a cheap white paint or coating of chalked lime that was used to quickly give a uniform clean appearance to a wide variety of surfaces, for instance, the entire interior of a barn.
In 1800 in the United States, the word was used in a political context, when a Philadelphia Aurora editorial said that "if you do not whitewash President Adams speedily, the Democrats, like swarms of flies, will bespatter him all over, and make you both as speckled as a dirty wall, and as black as the devil.“
- Encyclopædia Britannica