or 'ō·'ō

[ oh-oh ]
/ ˈoʊ oʊ /
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noun, plural o’·os.
any of several species of Hawaiian birds of the extinct genus Moho, especially the extinct M. nobilis (Hawaiian o'o), which had black plumage and two tufts of yellow plumes used to make ceremonial robes for the Hawaiian kings. The last surviving species was M. braccatus (Kauai o'o), classified as extinct in 1987.
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Origin of o'o

First recorded in 1885–90; from Hawaiian ʿōʿō

Other definitions for o'o (2 of 2)


a combining form meaning “egg,” used in the formation of compound words: oogamous.

Origin of oo-

<Greek ōio-, combining form of ōiónegg1
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022


What does oo- mean?

Oo- is a combining form used like a prefix meaning “egg.” It is used in many scientific terms, especially in biology.

Oo- comes from the Greek ōión, meaning “egg.” The Greek ōión helps form the word ōophóros, meaning “egg-bearing” and is the source of the combining form oophoro-, used to indicate the ovary.

Distantly related to the Greek ōión is the Latin word for egg, ōvum, source of the related combining forms ov-, ovi-, and ovo-, also used to mean “egg.” The Latin ōvum is ultimately the origin of ovario-, used, like oophoro-, to mean “ovary.”

What are variants of oo-?

When combined with words or word elements that begin with a vowel, oo- becomes o-, as in oidium.

Examples of oo-

One example of a scientific term that features the combining form oo- is oocyte, “an immature egg cell of the animal ovary,” including in humans.

The oo- part of the word means “egg,” as we have seen. The second part of the word is -cyte, from the Greek kýtos, means “cell.” Oocyte literally translates to “egg cell.”

What are some words that use the combining form oo-?

What are some other forms that oo- may be commonly confused with?

Not every word that begins with the exact letters oo- is necessarily using the combining form oo- to denote “egg.” Oodles, ooh, and ooze are three examples. Learn what oodles, ooh, and ooze mean and where they come from at our entries for the words.

Break it down!

The combining form -logy is used to name sciences or bodies of knowledge. What does oology, a branch of ornithology (science of birds), study?

How to use o'o in a sentence

British Dictionary definitions for o'o



combining form
egg or ovumoosperm

Word Origin for oo-

from Greek ōion egg 1
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Medical definitions for o'o


Egg; ovum:oogenesis.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.