|Easton's Bible Dictionary|
The Hermes (i.e., "the speaker") of the Greeks (Acts 14:12), a heathen God represented as the constant attendant of Jupiter, and the god of eloquence. The inhabitants of Lystra took Paul for this god because he was the "chief speaker."
Int. Standard Bible Encyclopedia
mur'-ku-ri, mer-ku'ri-us: The translation of Hermes, in Acts 14:12: "They called Barnabas, Jupiter; and Paul, Mercury, because he was the chief speaker." Hermes was the god of eloquence (and also of theft), the attendant, messenger and spokesman of the gods. The more commanding presence of Barnabas (compare 2 Corinthians 10:10) probably caused him to be identified with Zeus (the Roman Jupiter), while his gift of eloquence suggested the identification of Paul with Hermes (the Roman Mercury). The temple of Jupiter was before Lystra, and to him the Lycaonians paid their chief worship. Compare the legend of Baucis and Philemon (Ovid, Metam. viii.611).
See HERMES; JUPITER; GREECE, RELIGION IN ANCIENT.
M. O. Evans
Mercurius (1 Occurrence)
Acts 14:12 And they called Barnabas, Jupiter; and Paul, Mercurius, because he was the chief speaker. (KJV WBS)