Definitions

1. noun

A member of the phylum Cnidaria, specifically an animal that is closely related to jellyfish and corals and is usually attached to a substratum.

“The marine biologist spent years studying the unique life cycle of the freshwater hydroid.”

2. noun

A small, colonial hydroid, especially the genus Hydrocoryne, that is often found in tropical waters.

“The snorkeler marveled at the colorful hydroid colonies swaying gently in the ocean current.”