It's possible that:
* You might be thinking of a similar-sounding word. There are a few Welsh words that sound similar to "rhallt" but have different meanings. For example, "rhaid" means "must" or "have to", "rhaul" means "sun", and "rallt" means "a flood".
* It's a dialect word. Some words are only common in certain regions of Wales, so "rhallt" might be a regional word with a specific meaning.
* It's a misspelling. Perhaps you're looking for a different word entirely, and "rhallt" is a typo.
To help me understand your question better, could you please:
* Provide the context in which you saw the word "rhallt"?
* Tell me how the word was spelled?
* Can you remember any other words that were used around it?
Knowing more about where you saw the word will help me identify what you're looking for.