wet (one's) whistle
To have something to drink. I'm parched. I'm going to need to wet my whistle before we go on. If you're looking for Barney, he's down at the pub wetting his whistle.
wet one's whistle
Have a drink, as in I'm just going to wet my whistle before I go out on the tennis court. This expression uses whistle in the sense of "mouth" and may allude to the fact that it is very hard to whistle with dry lips. [Late 1300s]
wet one's whistle, to
To have a drink. It is very difficult to whistle with dry lips. An old children’s party game involves eating some dry crackers or bread and attempting to whistle; the first to succeed in doing so wins a prize. The term has been around since the fourteenth century. It appeared in Chaucer’s Canterbury Tales: “So was her joly whistle wel y-wet” (The Reeve’s Tale).