blackmail

Concise Oxford English Dictionary © 2008 Oxford University Press:
blackmail/ˈblakmeɪl/

▶noun the criminal offence of demanding money from someone in return for not revealing discreditable information.

■ the use of threats or unfair manipulation in an attempt to influence someone: emotional blackmail.

▶verb subject to blackmail.

– derivatives
blackmailer noun.

– origin C16 (denoting protection money levied by Scottish chiefs): from black + obs. mail ‘tribute, rent’, from ON mál ‘speech, agreement’.