vow n.

1580s, "appropriate by or as if by vow," from Latin devotus, past participle of devovere "dedicate by a vow, sacrifice oneself, promise solemnly," from de "down, away" (see de-) + vovere "to vow" (see vow (n.)). From c. 1600 as "apply zealously or exclusively." From 1640s as "to doom, consign to some harm or evil," and the word commonly had a negative sense in 18c.: The second and third meanings in Johnson's Dictionary (1755) are "to addict, to give up to ill" and "to curse, to execrate; to doom to destruction." Related: Devoted; devoting.

To devote indicates the inward act, state, or feeling; to dedicate is to set apart by a promise, and indicates primarily an external act; to consecrate is to make sacred, and refers to an act affecting the use or relations of the thing consecrated .... [Century Dictionary]

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.