1. A small diving waterbird of the grebe family, known for its ability to dive quickly and deeply underwater.
Usage: Also called a pied-billed grebe in North America; Informal or regional usage
2. A reckless or daring person, especially one who takes extreme risks.
Usage: Informal; Figurative use

Examples

• The helldiver disappeared beneath the water's surface in search of fish.
• We watched the helldiver pop up unexpectedly on the other side of the pond.
• That stunt driver is a real helldiver, always pushing the limits.
• The helldiver's compact body makes it perfectly adapted for underwater hunting.
• He earned a reputation as a helldiver for his fearless mountain climbing expeditions.