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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 á�����Dz�, 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 ���ܳ�ó��, “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 �������t¶��s That Use all- article.

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-?

• alloantibody
• allobaric
• alloerotism
• allogeneic
• allograph
• allopathy (using the equivalent form of allo- in German)
• allolalia
• allorhythmia
• allosome

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

• algo-
• allanto-
• alto-
• oleo-
• oligo-

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.

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