devout: [13] Essentially, devout and devote [16] are the same word; they come from an identical source, but reached English along different routes. That source is dēvōtus, the past participle of Latin dēvovēre, which was a compound formed from the intensive prefix dē- and vovēre ‘promise’ (source of English vote and vow). This entered English originally via Old French devot as an adjective, and was then reborrowed directly from Latin in the 16th century as the basis for a verb. => devote, vote, vow
devout (adj.)
early 13c., from Old French devot "pious, devoted, assiduous," from Latin devotus "given up by vow, devoted," past participle of devovere "dedicate by vow" (see devotion).