What does "dredge" mean?

Additional senses

1. 2.To catch or gather with a dredge; to deepen with a dredging machine. R. Carew. Dredging machine, a machine (commonly on a boat) used to scoop up mud, gravel, or obstructions from the bottom of rivers, docks, etc., so as to deepen them.
2. 3.A mixture of oats and barley. [Obs.] Kersey.
3. 4.To sift or sprinkle flour, etc., on, as on roasting meat. Beau. & Fl. Dredging box. (a) Same as 2d Dredger. (b) (Gun.) A copper box with a perforated lid; -- used for sprinkling meal powder over shell fuses. Farrow.