Origin and history of spellable

early 14c., spellen, "read letter by letter, write or say the letters of;" c. 1400, "form words by means of letters," said in most etymology sources to be from Anglo-French espeller, Old French espelir "to mean, signify; explain, interpret," also "spell out letters, pronounce, recite."

This French word is from Frankish *spellon "to tell" or some other Germanic source, from Proto-Germanic *spellam (source also of Dutch spellen, Old High German spellon "to tell," Old Norse spjalla, Gothic spillon "to talk, tell").

The native cognate word is Old English spellian, spillian "to tell, talk, speak, discourse." Only Barnhart seems to allow that the modern English word is partially from the Old English one, due to the difference in sense.

Klein's sources suggest a possible origin for this Germanic group in a PIE root *spel- (2) "to say aloud, recite, speak with emphasis" and cognates in Greek apeilē "threat" among other words, but Beekes finds the suggestion "rather far-fetched."

Also in early use speldren, from Old French espeldre, a variant of espelir. Related: Spelled; spelling.

In early Middle English still "to speak, preach, talk, tell," hence such expressions as hear spell "hear (something) told or talked about," spell the wind "talk in vain" (both 15c.). The meaning "form words with proper letters" is from 1580s.

Spell out "explain step-by-step" is recorded from 1940, American English. Shakespeare has spell (someone) backwards "reverse the character of, explain in a contrary sense, portray with determined negativity."

common termination and word-forming element of English adjectives (typically based on transitive verbs) with the sense "capable; liable; allowed; worthy; requiring; or bound to be ______ed," sometimes "full of, causing," from French -able and directly from Latin -abilis.

It is properly -ble, from Latin -bilis (the vowel being generally from the stem ending of the verb being suffixed), and it represents PIE *-tro-, a suffix used to form nouns of instrument, cognate with the second syllables of English rudder and saddle (n.).

A living element in English, used in new formations from either Latin or native words (readable, bearable) and also with nouns (objectionable, peaceable). Sometimes with an active signification (suitable, capable), sometimes of neutral signification (durable, conformable). By 20c. it had become very elastic in meaning, as in a reliable witness, a playable foul ball, perishable goods. A 17c. writer has cadaverable "mortal."

To take a single example in detail, no-one but a competent philologist can tell whether reasonable comes from the verb or the noun reason, nor whether its original sense was that can be reasoned out, or that can reason, or that can be reasoned with, or that has reason, or that listens to reason, or that is consistent with reason; the ordinary man knows only that it can now mean any of these, & justifiably bases on these & similar facts a generous view of the termination's capabilities; credible meaning for him worthy of credence, why should not reliable & dependable mean worthy of reliance & dependence? [Fowler]

In Latin, -abilis and -ibilis depended on the inflectional vowel of the verb. Hence the variant form -ible in Old French, Spanish, English. In English, -able tends to be used with native (and other non-Latin) words, -ible with words of obvious Latin origin (but there are exceptions). The Latin suffix is not etymologically connected with able, but it long has been popularly associated with it, and this probably has contributed to its vigor as a living suffix.