Old English spell "story, saying, tale, history, narrative, fable; discourse, command," from Proto-Germanic *spellam (see spell (v.1)). Compare Old Saxon spel, Old Norse spjall, Old High German spel, Gothic spill "report, discourse, tale, fable, myth;" German Beispiel "example." From c. 1200 as "an utterance, something said, a statement, remark;" meaning "set of words with supposed magical or occult powers, incantation, charm" first recorded 1570s; hence any means or cause of enchantment.
The term 'spell' is generally used for magical procedures which cause harm, or force people to do something against their will — unlike charms for healing, protection, etc. ["Oxford Dictionary of English Folklore"]
In general terms, the belief underlying the use of spells is that the wish that they embody will be fulfilled, regardless of its goodness or badness, so long as the formula has been correctly pronounced. Broadly speaking, then, spell and prayer, like magic and religion to which they severally belong, can be distinguished by the nature of the intended purpose. [Enyclopaedia Britannica, 1941]
Also in Old English, "doctrine; a sermon; religious instruction or teaching; the gospel; a book of the Bible;" compare gospel.
"fastened," mid-14c. in figurative sense of "compelled," earlier in fuller form bounden (c. 1300), past-participle adjective from bind (v.). Meaning "under obligation" is from late 15c.; the literal sense "made fast by tying (with fetters, chains, etc.)" is by 1550s. In philology, designating a grammatical element which occurs only in combination with others (opposed to free), from 1926. Smyth has man-bound (1867), of a ship, "detained in port for want of a proper complement of men."