Whet is a verb, and it means to rub on with something or to sharpen. You can whet a knife with stone, for example. It can also mean to excite, stimulate or instigate.
There’s nothing like a global financial crisis to whet appetites for business news. (USA Today)
Mr. Lawrence said the problems had contributed to the scarcity of the machines. He said, however, that the shortages had helped whet public demand. (NY Times)
