spell vs unspell

spell is a noun but unspell is not a noun.

Word	Noun	Adjective	Verb	Adverb
spell	Yes	No	Yes	No
unspell	No	No	Yes	No

spell (noun)	unspell (noun)
a verbal formula believed to have magical force
a psychological state induced by (or as if induced by) a magical incantation
a time period for working (after which you will be relieved by someone else)
a period of indeterminate length (usually short) marked by some action or condition

spell (verb)	unspell (verb)
take turns working	release from a spell
orally recite the letters of or give the spelling of
indicate or signify
place under a spell
write or name the letters that comprise the conventionally accepted form of (a word or part of a word)
relieve (someone) from work by taking a turn