c. 1400, from Old French loialte, leaute "loyalty, fidelity; legitimacy; honesty; good quality" (Modern French loyauté), from loial (see loyal). The Medieval Latin word was legalitas. The earlier Middle English form was leaute (mid-13c.), from the older French form. Loyalty oath first attested 1852.
Allegiance ... is a matter of principle, and applies especially to conduct; the oath of allegiance covers conduct only. Loyalty is a matter of both principle and sentiment, conduct and feeling; it implies enthusiasm and devotion .... [Century Dictionary, 1897]
mid-14c., also simply coat (mid-14c.); originally a tunic embroidered or painted with heraldic armorial bearings (worn over armor, etc); see coat (n.) + arm (n.2) and compare Old French cote a armer. Sense transferred in Middle English to the heraldic arms themselves. Hence turncoat, one who put his coat on inside-out to hide the badge of his loyalty (1550s).
"want of loyalty, unfaithful behavior," early 15c., disloialte, from a variant of Old French desloiaute, desleauté "disloyalty, faithlessness, marital infidelity," from desloial, desleal "treacherous, false, deceitful" (Modern French déloyal), from des- "not, opposite of" (see dis-) + loial "of good quality; faithful; honorable; law-abiding; legitimate, born in wedlock," from Latin legalem, from lex "law" (see legal). Since c. 1600 especially "violation of allegiance or duty to a state or sovereign."
c. 1200, devocioun, "profound religious emotion, awe, reverence," from Old French devocion "devotion, piety" and directly from Latin devotionem (nominative devotio), noun of action from past-participle stem of devovere "dedicate by a vow, sacrifice oneself, promise solemnly," from de "down, away" (see de-) + vovere "to vow" (see vow (n.)). From late 14c. as "an act of religious worship, a religious exercise" (now usually devotions).
In ancient Latin, "act of consecrating by a vow," also "loyalty, fealty, allegiance;" in Church Latin, "devotion to God, piety." The application to secular situations came to English via Italian and French; sense of "act of setting apart or consecrating" is from c. 1500.