Which word means to make known, especially a secret?

The term that means to make known, especially a secret, is "divulge." This word specifically conveys the action of sharing information that is meant to be kept private or confidential. When someone divulges a secret, they are revealing details that are not generally known, which aligns closely with the essence of the question.

While "disclose," "discover," and "reveal" do carry similar connotations, they each have nuances that differentiate them. "Disclose" is often used in legal or formal contexts to indicate the act of uncovering information but does not necessarily imply that the information was secretive. "Discover" implies the act of finding something that was hidden or unknown rather than communicating it to others. "Reveal" is a broader term that can relate to showing or making something visible, but it does not specifically underscore the aspect of confidentiality as strongly as "divulge" does. Therefore, "divulge" is the most precise term for making known something that was a secret.