waterproof

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Impervious to or unaffected by water.
• adjective Made of or coated or treated with rubber, plastic, or a sealing agent to prevent penetration by water.
• noun A material or fabric that is impervious to water.
• noun Chiefly British A raincoat or other such outer garment.
• transitive verb To make impervious to water.

from The Century Dictionary.

• To render impervious to water, as cloth, leather, etc.
• Impervious to water, or nearly so
• noun Any material which repels water; especially, a light woolen cloth made for the purpose, and subjected to some waterproofing application.
• noun A garment of some material that repels water, made either of waterproof , or of mackintosh or a similar material made with india-rubber.

from the GNU version of the Collaborative International Dictionary of English.

• transitive verb To render impervious to water, as cloth, leather, etc.
• adjective Proof against penetration or permeation by water; impervious to water.
• noun A substance or preparation for rendering cloth, leather, etc., impervious to water.
• noun Cloth made waterproof, or any article made of such cloth, or of other waterproof material, as rubber; esp., an outer garment made of such material.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Unaffected by water.
• adjective Made of or covered with material that doesn't allow water in.
• verb To make waterproof or water-resistant.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a water-resistant coat
• adjective not permitting the passage of water
• noun any fabric impervious to water
• verb make watertight