pretending to be sb else in order to do sth secretly; hidden or acting in secret, shielded by darkness or by staying out of sight
Oxford75% of films
pretending to be sb else in order to do sth secretly
We'll keep Williams under cover, until we can break the story...
Editorial25% of films
hidden or acting in secret, shielded by darkness or by staying out of sight
load the cash under cover.
Definitions from the Oxford Advanced Learner's Dictionary, 9th edition