1. Something that confirms, ratifies, or makes secure. 2. An amount of water standing in a drain trap to prevent foul air from rising; see Trap Seal. 3. Close securely or hermetically. 4. Apply a non-porous coating to a surface to make it impervious. 5. A counterflashing closure strip, narrow in shape, made of bituminous materials. 5. To secure a roof from the entry of moisture.