Old English is a Germanic language that was spoken in England from roughly the 5th to the 12th centuries. It's the precursor to Modern English and has a distinct vocabulary and grammatical structure.
It's possible you might be thinking of a different word, or that you're remembering a word from a different language that resembles "fum."
To help me understand what you're looking for, could you please provide more context? For example:
* Where did you encounter this word? (A book, a movie, a conversation?)
* What was the surrounding text or conversation?
* What do you think it might mean?
With more information, I can better assist you in finding the correct word or understanding its meaning.