The Collaborative International Dictionary of English v.0.48:
Hush \Hush\, n. Stillness; silence; quiet. [R.] "It is the hush of night." --Byron. [1913 Webster] Hush money, money paid to secure silence, or to prevent the disclosure of facts. --Swift. [1913 Webster]WordNet (r) 3.0 (2006):
hush money n 1: a bribe paid to someone to insure that something is kept secret