These "look-alikes" are sometimes confused despite the fact that they are antonyms. Covert means "covered," "sheltered," "hidden," "secret," "concealed"; overt means "open to view," "plain," "manifest," "apparent," "public." To keep them distinguished, associate overt with open and covert with cover: "His every act and aim was overt, a matter of public record." "These politicians entered into a covert agreement about the paving contracts."
Dictionary of problem words and expressions. Harry Shaw. 1975.