1. a plan or action to mask a truth
a big cover-up
A 'cover-up' can literally mean something used to cover a part of the body or to cover an object: "Women must wear a cover-up over any revealing clothing when entering the Synagogue." In this usage, it can refer to something worn over a swimsuit or clothes used for exercising to preserve dignity or to keep warm. 'A cover-up' can also mean actions taken to obscure the truth or to mask the facts in a situation: "The church attempted a cover-up of abuses that came to light years later." This use of the phrase is more likely to be used in formal situations or in printed reports. Similar expressions include 'to whitewash' and 'to conceal.'