Comfort before difficulty
Today easy is the ordinary opposite of hard: a task that asks for little skill or strain. Speakers also still rest easy, sit in an easy chair, or take it easy, where comfort and unhurried calm remain audible. That split is the history in miniature. The adjective entered English as a word about being at ease. Only later did it become the default way to say that something is not difficult.
A French past participle
The form English inherited is a borrowing, not a native Germanic survivor. Around 1200, Middle English writers used spellings such as esy and eesy. Those match Old French aisié (modern French aisé): comfortable, at ease, even well-off. The French adjective is the past participle of aisier, to put someone at ease, built on the noun aise, which covered comfort, pleasure, opportunity, and the room to move.
Anglo-Norman, the French of post-Conquest England, carried the same family under many spellings, among them eisé and ese. The Oxford English Dictionary treats easy as a French loan, with French etyma along the lines of esé and aisié. The American Heritage Dictionary analyzes a related Old French verb aaisier as the prefix a- (from Latin ad, to) plus aise. Historical dictionaries also note a parallel English path: once the noun ease was in the language, speakers could add the native adjective suffix -y. Ease plus -y and the borrowed participle then blended into one word. The development of English senses was shaped by that noun as well as by the participle.
Where French aise itself came from
Here the trail should stay uncertain. Old French aise meant elbow room as well as comfort: space at one’s sides, then opportunity, then well-being. Related Romance words include Provençal ais, Italian agio, and Portuguese azo. They look like a family even if the exact Latin parent is disputed.
A derivation favored in more recent English and French dictionaries starts from Latin adiacens, lying near, the present participle of adiacere, to lie beside or border on, the same root as adjacent. Calvert Watkins and several modern handbooks take that route. The musical term adagio, from Italian ad agio, at leisure, is often cited as a cousin if the Latin etymology is right. Older scholarship raised phonetic and semantic objections. Another proposal, associated with Sophus Bugge, starts from Latin ansa, a handle, via a vulgar form asa, with a figurative step from handle to opportunity, or from arms akimbo to elbow room. A further nineteenth-century idea made aisance the oldest French form, from medieval Latin adjacentia, and treated aise as a later back-formation. None of these accounts is airtight. Easy sits on a French word whose deeper Latin, or possibly non-Latin, source is still argued.
The native word it replaced
English did not lack a word for not difficult. Old English had īeþe as an adjective and ēaþe as an adverb. They belong to a West Germanic set: Old Saxon ōþi, Old High German ōdi, Old Norse auðr and the prefix auð-. Icelandic still uses auð- in compounds with the sense easy. The same Germanic material later yields German öde, empty or desolate, though that semantic jump is itself debated. In later English the native adjective survives mainly as dialectal eath, eathe, or Scots eith.
Wiktionary and older historical dictionaries treat this native line as having merged with, or colored, the French loan. That helps explain why a word whose first English senses were about comfort and being well-off became, by the late thirteenth century, the ordinary adjective for a task that takes no great labor. So the origin of the word easy is not a story about difficulty at all, but about a comfort word that took over a job English already had.
Senses that piled up
Once the adjective was in Middle English, its meanings fanned out in a clear order. Comfort and freedom from anxiety come first, around 1200. Not difficult follows in the late 1200s. Early in the fourteenth century it describes conditions that offer comfort. Late in that century it describes people: lenient, kind, calm, gentle. By the 1610s it can mean readily yielding, not hard to persuade, a sense that later feeds informal and often derogatory uses for sexual availability. Finance once used it of a market that was not tight. An older social sense, still heard in rest easy, is now rare except in set phrases.
Set phrases keep the comfort strand alive. At ease is recorded from the late fourteenth century and later becomes a military command, from 1802, meaning drop the stiffness. Be easy in the sense relax is recorded from 1746; take it easy from 1804; easy does it from 1835. Nineteenth-century American English adds easy money, by 1889, and Easy Street, from 1890. The radio format easy listening is mid-twentieth century. Comparative easier and superlative easiest are the regular English grades.
Cognates on the Romance side still look like the source: French aisé remains an everyday word for well-off or effortless. On the Germanic side, the lost native adjective is the better reminder that English once had a different word for the same job.
A small leftover
If you want one fact to keep, keep the native rival. Before French aisié took over, speakers already said īeþe. Easy did not invent the idea of little effort. It borrowed a comfort word and, over a century or so, taught it to do the work of an older English adjective that now lives on only in dialect.