n. & v.
n. 1 a an extortion of payment in return for not disclosing discreditable information, a secret, etc. b any payment extorted in this way. 2 the use of threats or moral pressure.
v.tr. 1 extort or try to extort money etc. from (a person) by blackmail. 2 threaten, coerce. blackmailer n.
[ BLACK + obs. mail rent, OE mal f. ON m l agreement ]