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a combining form meaning “other,” used in the formation of compound words (allotrope) and in chemistry to denote the more stable of two geometric isomers.
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Also (except in chemistry), especially before a vowel, all- .

Origin of allo-

<Greek, combining form of állos other; cognate with Latin alius,else

Other definitions for allo- (2 of 2)


Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022


What does allo- mean?

Allo- is a combining form used like a prefix meaning “other” or “different.” It is frequently used in a variety of medical and scientific terms.

In chemistry, allo- denotes the more stable of two geometric isomers. Isomers are molecules that contain the same numbers of the same kinds of atoms but in which the atoms have different structural arrangements.

Allo- comes from Greek állos, meaning “other.” This word’s distant cousins in Latin, alius and alter, which have similar definitions, give us words such as alien and alternative. The opposite of allo- is the form auto-, from Greek autós, “self.”

What are variants of allo-?

When combined with words or word elements that begin with a vowel, allo- typically becomes all-, as in allonym.

Want to learn more? Read our Words That Use all- article.

Examples of allo-

One example of a scientific term that features the combining form allo- is allogamy, “cross-fertilization in plants (opposed to autogamy).”

We know allo- means “other,” so what about the -gamy portion of the word? The form -gamy has a variety of meanings, including “fertilization,” “pollination,” or even “marriage” in certain contexts. Allogamy literally translates to “other fertilization,” that is, when a flower of one kind of plant is fertilized from the flower of a different kind of plant.

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

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

Not every word that begins with allo- is using the combining forming allo- to denote “other.” Learn why allocate means “distributed” at our entry for the word.

Break it down!

An autograph is a person’s own signature. Based on the meanings of allo- and autograph, what is an allograph?

How to use allo- in a sentence

British Dictionary definitions for allo-


before a vowel all-

combining form
indicating difference, variation, or oppositionallopathy; allomorph; allophone; allonym

Word Origin for allo-

from Greek allos other, different
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 allo-


Other; different:allotransplantation.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.