caulk

Concise Oxford English Dictionary © 2008 Oxford University Press:
caulk /kɔːk/ (US also calk)

▶noun a waterproof filler and sealant, used in building work and repairs. ▶verb

• 1 seal with caulk.

• 2 make (a boat or its seams) watertight.

– derivatives
caulker noun.

– origin ME (in the sense ‘copulate’, used of birds): from Old North. Fr. cauquer, caukier, var. of cauchier ‘tread, press with force’, from L. calcare ‘tread’, from calx, calc- ‘heel’.