Definition of hydroid in English:

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Pronunciation: /ˈhīdroid/


A coelenterate of an order that includes the hydras. They are distinguished by the dominance of the polyp phase.
  • Order Hydroida, class Hydrozoa.
Example sentences
  • Aside from its temporary and permanently resident fish, the underside is decorated with sponges, hydroids, tunicates, tube worms, cup corals and anemones.
  • There were dense walls of soft corals, sponges, anemones and hydroids, nudibranchs, creepy-crawlies and lots of fish.
  • On the walls are a riot of soft corals, sponges, hydroids and anemones in all shapes and sizes.


1Relating to coelenterates of the hydroid group.
Example sentences
  • He had shown that hydroid jellyfish known as naked-eyed medusae reproduce not only by spewing eggs, but also by asexual budding, which he found marvelous to behold.
  • The hydroid tissues, in particular, are the general run of moss water storage cells and are probably only remotely related to the xylem of tracheophytes.
  • Before long, similar green proteins were detected in many bioluminescent coelenterates including various medusae, apparently all luminescent hydroid polyps, and a few others.
1.1 another term for polypoid (sense 1).


Mid 19th century: from hydra + -oid.

For editors and proofreaders

Syllabification: hy·droid

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