Difficult
late Middle English: back-formation from difficulty.
wiktionary
From Middle English difficult (ca. 1400), a back-formation from difficultee (whence modern difficulty), from Old French difficulté, from Latin difficultas, from difficul, older form of difficilis(“hard to do, difficult”), from dis- + facilis(“easy”); see difficile. Replaced native Middle English earveþ(“difficult, hard”), from Old English earfoþe(“difficult, laborious, full of hardship”), cognate to German Arbeit(“work”).
etymonline
difficult (adj.)
c. 1400, "not easy, requiring or dependent on effort; troublesome, arduous," apparently an unetymological back-formation from difficulty. French has difficile, Latin difficilis. Of persons, "hard to please," from 1580s. Related: Difficultly.
