Hello Chanmonchannon,
I’ve only just seen your question now, but I’ll try to answer it. :-)
The three words you ask about are extremely rare. In fact, I don’t think I have ever heard them before! I am not surprised you could not easily find the definitions. Here are the definitions I have found for the other two words:
hyphaeresis
n. omission of sound, syllable or letter from word.
That is, hyphaeresis happens when a part of a word is missing. It is not there.
numnuh
n. A pad that goes under the saddle to keep the saddle clean and to cushion the horse’s or pony’s back.
Also Known As: saddle pad, pad, saddle blanket
Examples: The wool numnah protected the saddle and cushioned the horse’s back.
However, the meanings of the words are not what matter the most! In a spelling bee, it is common for judges to ask the young people to spell very complex and unusual words. It makes the competition more difficult. I hope that explanation helps!