Origin and history of adagio

early 15c., "contiguous, bordering; close, nearby," from Latin adiacentem (nominative adiacens) "lying at," present participle of adiacere "lie at, border upon, lie near," from ad "to" (see ad-) + iacēre "to lie, rest," related to iacere "to throw; to lay" (from PIE root *ye- "to throw, impel"). Only of things, never of persons or animals. Adjacent, properly, is near but not necessarily in contact; adjoining is so as to touch. Latin adiacentia meant "the neighborhood."

c. 1200, "physical comfort, undisturbed state of the body; tranquility, peace of mind," from Old French aise "comfort, pleasure, well-being; opportunity," which is of uncertain origin. According to Watkins is ultimately from Latin adiacens "lying at," present participle of adiacere "lie at, border upon, lie near," from ad "to" (see ad-) + iacere "to lie, rest," literally "to throw" (from PIE root *ye- "to throw, impel"). Recent dictionaries in English and French seem to support this derivation, though older sources found objections to it. Compare adagio.

At ease "at rest, at peace, in comfort" is from late 14c.; as a military order (1802) the word denotes "freedom from stiffness or formality."