The prefix inter- means between or among. The prefix intra- means within. So, for example, an interstate highway is a highway that goes between or among states, while an intrastate highway is one that exists only within a single state.
Intra- and inter- can be attached to any common noun without a hyphen—although, as the below examples show, many writers aren’t comfortable doing so. Your spell check may catch your unhyphenated inter-/intra- coinage, but spell check is often wrong.
Examples
Here are a few examples to demonstrate the difference between the prefixes:
If he survives the current unrest, his regime will still be weakened, and the president’s apparent hopes for an intra-family handoff of power to his son will fall into doubt. [New Yorker]
Gnomeo is no longer a bystander to the inter-family feud, but instead is a leader of the movement against the Capulets. [Technique]
But Cameron’s declared ambition for the “complete modernisation” of public services could prove increasingly divisive and stimulate intra-national tensions across the UK. [Guardian]
The past year for Asia was one characterized by high economic growth and increased international tensions, with China at the center of both trends. [Honolulu Star-Advertiser]
A hyphen is necessary when the prefix is affixed to a proper noun—for example:
The news agency close to Hamas reports that at a mass demonstration yesterday in Ramallah demanding an end to the intra-Palestinian schism … [MEMRI]
As with so many other inter-Korean meetings in the nearly 60 years since the Korean War, nothing substantively changed … [Wall Street Journal]
