It’s strange how relatively unconnected words often end up with the same spelling. Take the word spell, itself: there are 5 nouns and 6 verbs with that letter sequence, all with separate superscripts, which indicates that they have varying etymologies.
Spell-1 started as discourse, narration, speech. It drifted organically into a sermon, which sheds light on the word gospel as coming from good spell-- good message. By the 16th century, it was an incantation, then an enthralling charm.
Coming from a different source, spell-2 was variously defined as a splinter, a chip, a fragment, a bar, a rail, or a rung.
Spell-3 named a relief-gang or work shift, and later an interval of relaxation. Then it was a period of time of indefinite length. It became a weather term (dry spell), and in the 19th century signified a fit, an attack of nervous excitement (fainting spell).
Spell-4 gets around to the common meaning of the term: a way or mode of spelling a word.
The last noun meaning, spell-5, signifies a playhouse or theater.
Turning to the verb forms, spell-1 meant to speak or to preach. Spell-2 meant to read something slowly and deliberately, letter by letter. It drifted into to decipher or to contemplate. Then it meant to write something letter by letter in a prescribed order. To suggest a desire for something was yet another variation.
Spell-3 means to relieve someone at work. It also means to take an interval of rest. Spell-4 means to bewitch or to invest with magical qualities. Spell-5 meant to allow a sail to lie loose in the wind. Spell-6 meant to fit with bars and cross-pieces, or to splinter.
Now I have to go rest a spell.
SIDEBAR: Spell: the band
SIDEBAR: spelling rules
Coming soon from McFarland & Co.: Word Parts Dictionary, 2nd edition