Inter vs. Intra: Learning the Difference

Even though inter and intra are both Latin prefixes, they have almost opposite definitions. The basic meanings of these words are:

• inter - between or among
• intra - within or inside

Words that begin with inter describe connections between objects, groups or ideas. However, words that begin with intra indicate something inside of a group or within an object. You can probably see why mixing these words up would be confusing! The key to knowing which one to use depends on the context of your sentence and what you are truing to say.

You use inter when describing an action that goes between two groups or objects. For example, "international relations" refers to the relations between two or more countries, and an "interstate" is a highway that connects two or more states.

More examples of the prefix inter include:

• interaction - action that occurs between people or objects
• intercom - communication between a microphone and a loudspeaker
• intermission - the break between acts
• intersection - point where two lines (often streets) cross
• interval - the space between two events
• intervene - to come between

You can probably think of a dozen more examples of this popular prefix. In most cases, they are describing the relationship between or among two nouns. The prefix intra wouldn't work if you substituted it in these words.

Intra is a prefix that you use when describing an action that happens within or inside a noun. It can refer to activities within a group or a verb happening inside of a singular noun. You're most likely to see words that begin with intra in the science or medical fields.

Words that use the word intra include:

• intracranial - inside the skull
• intradermal - within the skin layer
• intramarginal - within the margins
• intramural - within a school or institution
• intranasal - inside the nose
• intravenous - inside the vein

Now that you've seen examples of words that use inter and intra, you can see that they are definitely not interchangeable. There are even some words that completely change meaning when you add the other prefix! Some of these words include:

• interdisciplinary - connections between two or more academic disciplines
• intradisciplinary - within one academic discipline

• intergalactic - relationship between galaxies
• intragalactic - an event occurring within one galaxy

• interpersonal - relationship between people
• intrapersonal - something that exists within one person

• intermuscular - two or more muscles working in a complex movement
• intramuscular - inside of one muscle

• internet - connection between computer networks
• intranet - one computer network inside an institution or organization

• interstate - crossing between two or more states
• intrastate - occurring within the borders of one state

So if these prefixes are so different, why do they get confused all the time? It's an understandable mistake, not only because the words sound so similar, but because of another Latin root: internal, which means "inside." Intra evolved from the earlier Latin word internus, which also means "inside," as opposed to the existing Latin root inter.

It's easy to see why they get confused. If you're sending an internal memo, you only want people in your office to see it. But a grammar mistake might lead you to believe that it's an interoffice memo, since both words start with inter. Sending an interoffice memo would send the message between offices, not just inside your own office. Therefore, an internal memo is the same thing as an intraoffice memo.

Some people believe that words beginning with inter and intra, such as "intramural" or "interactive," should be hyphenated as "intra-mural" and "inter-active." But like all words with prefixes, you don't need a hyphen between the affix and the word. Words that include inter and intra are not compound words, and therefore wouldn't need a hyphen.

Knowing the difference between inter and intra can keep you from making an embarrassing — or life-threatening, if you're a doctor — mistake in the workplace. If you'd like to clear up any more vocabulary misunderstandings, check out the difference between emigrate and immigrate. Learning how to use among vs. amongst might also be useful. You can also avoid showing up for the wrong meal if you know how to tell supper and dinner apart.