IPA: //ˈɡriːnˌmeɪl//
KK: /ˈɡriːnˌmeɪl/
The act of purchasing a large amount of a company's shares to create a threat of takeover, then selling those shares back to the company for a higher price than what they are worth.
The investor engaged in greenmail to profit from the company's fear of a takeover.
Greenmail is a portmanteau formed from "green" (meaning the color associated with money) and "blackmail" (from Old English "mæl", meaning a payment or tribute). The term refers to a practice where a company buys back its shares at a premium to prevent a hostile takeover, thus relating to financial coercion.
Think of 'green' representing money and 'blackmail' as a form of coercion — greenmail is essentially using money to prevent a takeover.