If you saw it in a specific context, I can help you decipher its meaning if you provide more information:
* Where did you see it? (Book, website, conversation, etc.)
* What was the context? (What was the sentence or paragraph about?)
Without more context, it's difficult to say what "sunhigh" might mean. It could be a figurative expression related to the sun being high in the sky, or it could be a technical term specific to a particular field.