It's likely a misspelling or a made-up phrase.
Possible interpretations:
* Typo: It could be a misspelling of a French phrase like "Cherche un intrus" (look for an intruder), "Cherche intrus" (look for an intruder), or "Cherche-t-il un intrus?" (Is he looking for an intruder?).
* Slang: It might be a slang term in a specific region or community that isn't widely known.
* Invented phrase: It could be a fictional phrase created for a specific purpose, like a game or a story.
To understand what it means, you'll need more context:
* Where did you encounter this phrase? (book, online, conversation, etc.)
* What was the surrounding text or conversation?
Providing more information will help me understand the meaning of "cherche rintrus."