Dropper \Drop"per\, n.

1. One who, or that which, drops. Specif.: (Fishing) A fly that drops from the leaden above the bob or end fly.

2. A dropping tube.

3. (Mining) A branch vein which drops off from, or leaves, the main lode.

4. (Zo["o]l.) A dog which suddenly drops upon the ground when it sights game, -- formerly a common, and still an occasional, habit of the setter.

Source: Webster's Revised Unabridged Dictionary (1913)