The Greek proper noun Zeus (Ζεύς) is the name of the chief god of the Greek pantheon, the sky-father and king of the Olympian gods. It appears twice in the NT — Acts 14:12 and 14:13 — both in the account of Paul and Barnabas at Lystra, where the locals mistook them for gods and called Barnabas 'Zeus' and Paul 'Hermes.'
When Paul healed a man lame from birth at Lystra (Acts 14:8–18), the crowd, speaking in the Lycaonian language, declared 'The gods have come down to us in the likeness of men!' They identified Barnabas as Zeus — perhaps because of his commanding appearance — and Paul as Hermes 'because he was the chief speaker.' The priest of Zeus, whose temple was at the entrance of the city, brought oxen and garlands to offer sacrifice. Paul and Barnabas tore their garments in horror and redirected the crowd to 'the living God, who made the heaven and the earth.' The scene vividly illustrates the clash between Greco-Roman polytheism and apostolic monotheism.