spelldown vs spelling bee

spelldown and spelling bee both are nouns.

Word	Noun	Adjective	Verb	Adverb
spelldown	Yes	No	No	No
spelling bee	Yes	No	No	No

As nouns, spelldown and spelling bee are synonyms defined as:

spelldown and spelling bee: a contest in which you are eliminated if you fail to spell a word correctly

Other synonyms of spelldown include spelling contest.

spelldown (noun)	spelling bee (noun)
a contest in which you are eliminated if you fail to spell a word correctly	a contest in which you are eliminated if you fail to spell a word correctly