greenmailPronunciation: /ˈgriːnmeɪl/Definition of greenmail noun [mass noun] Stock Exchange the practice of buying enough shares in a company to threaten a takeover, forcing the owners to buy them back at a higher price in order to retain control. Derivatives greenmailer noun Origin: 1980s: blend of green and blackmailgreenmail in other Oxford dictionaries Definition of greenmail in the US English dictionary