sea oak

noun

1

: any of various rockweeds (especially Fucus vesiculosus and F. serratus)

2

British : a sertularian hydroid (Dynamena punila) that forms a small much-branched arborescent colony with a tough horny skeleton into which the polyps can contract

Love words?

You must — there are over 200,000 words in our free online dictionary, but you are looking for one that’s only in the Merriam-Webster Unabridged Dictionary.

Start your free trial today and get unlimited access to America's largest dictionary, with:

• More than 250,000 words that aren't in our free dictionary
• Expanded definitions, etymologies, and usage notes
• Advanced search features
• Ad free!