late 14c. as a term of reproach for a corrupt or lax prelate, from the Roman surname, especially that of Pontius Pilate, a governor of the Roman province of Judaea under Tiberius, from Latin Pilatus, literally "armed with javelins," from pilum "javelin" (see pile (n.2)).
Other than having presided over the trial of Jesus and ordering his crucifixion, little is known of him. In Middle English pilates vois was "a loud, boastful voice," of the sort used by Pilate in the mystery plays. Among slang and cant uses of Pontius Pilate mentioned in the 1811 "Dictionary of Buckish Slang, University Wit and Pickpocket Eloquence" is "(Cambridge) a Mr. Shepherd of Trinity College; who disputing with a brother parson on the comparative rapidity with which they read the liturgy, offered to give him as far as Pontius Pilate in the Belief."
c. 1300, saveour, "one who delivers or rescues from peril," also a title of Jesus Christ, from Old French sauveour, from Late Latin salvatorem (nominative salvator) "a saver, preserver," originally and chiefly Church Latin, with reference to Christ (source also of Spanish salvador, Italian salvatore), from salvatus, past participle of salvare "to save" (see save (v.)). In the New Testament used of both Jesus and God.
In the Christian sense, the Latin noun is a translation of Greek sōtēr "savior." In English, it replaced Old English hælend, literally "healing," likely a loan-translation from Latin, a noun use of the present participle of hælan (see heal). Middle English also had salvatour "Jesus Christ," also "a rescuer" (c. 1300) from the Latin, and compare saver. The conservatism of liturgy sustained the -our spelling (see -or).
The old spelling saviour still prevails even where other nouns in -our, esp. agent-nouns, are now spelled with -or, the form savior being regarded by some as irreverent. [Century Dictionary, 1895]
Old English godspel "glad tidings announced by Jesus; one of the four gospels," literally "good spell," from god "good" (see good (adj.)) + spel "story, message" (see spell (n.1)). A translation of Latin bona adnuntiatio, itself a translation of Greek euangelion "reward for bringing good news" (see evangel). The first element of the Old English word originally had a long "o," but it shifted under mistaken association with God, as if "God-story" (i.e. the history of Christ).
The mistake was very natural, as the resulting sense was much more obviously appropriate than that of 'good tidings' for a word which was chiefly known as the name of a sacred book or of a portion of the liturgy. [OED]
The word passed early from English to continental Germanic languages in forms that clearly indicate the first element had shifted to "God," such as Old Saxon godspell, Old High German gotspell, Old Norse goðspiall. Used of anything as true as the Gospel from mid-13c.; as "any doctrine maintained as of exclusive importance" from 1650s. As an adjective from 1640s. Gospel music is by 1955. Gospel-gossip was Addison's word ("Spectator," 1711) for "one who is always talking of sermons, texts, etc."