caulk also calk 
(kôk)
(kôk)v. caulked, caulk·ing, caulks also calked or calk·ing or calks
v.tr.
1. To make watertight or airtight by filling or sealing: caulk a pipe joint; caulked the cracks between the boards with mud.
2. Nautical To make (a boat) watertight by packing seams with a waterproof material, such as oakum or pitch.
v.intr.
To apply caulking: caulked all around the window frame.
n.
Caulking.
[Middle English cauken, to press, from Old North French cauquer, from Latin calcāre, to tread, from calx, heel.]
caulker n.