spelldown vs spelling contest

spelldown and spelling contest both are nouns.

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

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

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

Other synonyms of spelldown include spelling bee.

spelldown (noun)	spelling contest (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