Pronunciation: (pen'i-trunt),[key] —n. 1. a person or thing that penetrates.
2. a compound that penetrates the skin, as a lotion or cream.
3. a substance that lowers the surface tension of water; wetting agent.
4. Zool.a large nematocyst discharging a barbed thread that penetrates the body of the prey and injects a toxic fluid.