1. a substance or treatment used to make something waterproof
2. a person who applies waterproofing treatments

Examples

• She applied a waterproofer to her hiking boots before the camping trip.
• The contractor recommended a high-quality waterproofer for the basement walls.
• This fabric waterproofer will keep your jacket dry in heavy rain.
• The waterproofer arrived early to seal the deck before the storm.
• We need to buy a waterproofer for the tent seams.
• The professional waterproofer guaranteed his work for five years.