spell down, to outspell others in a spelling match.
9.
spell out,
a.
to explain something explicitly, so that the meaning is unmistakable: Must I spell it out for you?
b.
to write out in full or enumerate the letters of which a word is composed: The title “Ph.D.” is seldom spelled out.
Origin: 1250–1300; Middle English spellen < Old French espeller < Germanic; compare Old English spellian to talk, announce (derivative of spellspell2), Old High German -spellōn,Old Norse spjalla,Gothic spillōn
"work in place of (another)," O.E. spelian "to take the place of," related to gespelia "substitute," of uncertain origin. Perhaps related to spilian "to play" (see spiel). The noun meaning "indefinite period of time" first recorded 1706.