The Collaborative International Dictionary of English v.0.48:

Caulk \Caulk\, v. t.
   1. See Calk, v..
      [1913 Webster]

   2. to fill in the seams or cracks of, with a waterproof
      material such as caulk.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Caulk \Caulk\, n.
   1. See Calk.
      [1913 Webster]

   2. a viscous semisolid material of varying composition used
      to fill in seams of objects which are exposed to water,
      such as wooden ships or bath tiles; -- called also calk
      and caulking. After applying in a semisolid form, the
      material hardens and dries to form a waterproof seal. It
      is used in the process of caulking. It is sometimes
      applied together with a rope-like cord to fill larger
      seams.
      [PJC]

WordNet (r) 3.0 (2006):

caulk
    n 1: a waterproof filler and sealant that is used in building
         and repair to make watertight [syn: caulk, caulking]
    v 1: seal with caulking; "caulk the window" [syn: caulk,
         calk]

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "caulk":
   bar, bind, block, block up, blockade, bung, chink, choke,
   choke off, choke up, clog, clog up, congest, constipate, cork,
   cover, dam, dam up, fill, fill up, foul, jam, obstipate, obstruct,
   pack, plug, plug up, spile, stanch, stay, stench, stop, stop up,
   stopper, stopple, stuff, stuff up