spell names words thought to have magic power or to make a piece of magic work, and also a short period of time during which something lasts; as a verb, it means to say or write the letters of a word in the correct order.
Oxford gives four noun senses. Two concern time: a short period during which something lasts, as in a spell of warm weather, and a period spent doing something or working somewhere. The other two concern 📝magic: the words themselves, or the piece of magic that happens when they are said, which can be cast on somebody and leave them under a spell; and, figuratively, a quality so attractive or interesting that it has a strong influence on others, as in falling under someone's spell.
As a verb, spell also means to form words correctly from individual letters, and, of letters, to form a word when put together in order. It can mean to have something, usually something bad, as a result, as when a crop failure spells disaster. In informal North American English, to spell somebody is to replace them for a short time so that they can rest.
The noun families have separate origins. The magical senses come from Old English spel(l), "narration", of Germanic origin; the time senses date from the late 16th century as a variant of dialect spele, "take the place of", of unknown origin. The verb is a Middle English shortening of Old French espeller.