The Septuagint is the Greek translation of the Old Testament from Hebrew. It tells the story of Naaman, the Syrian leper, who was told by the prophet Elisha to dip seven times in the Jordan River for healing. The translation reads, "Then Naaman went down and baptizo himself seven times in the Jordan according to the saying of the man of God."
Flavius Josephus was an illustrious Jewish historian who wrote, "The servants of Herod took Aristobulus out in the middle of the pool and they baptizo, baptizo, and baptizo him until they drowned him." They did not accomplish that by pouring or sprinkling water onto him.
Modern Greek is practically the same speech as it was in the ancient world. The Greek language has changed less in 2,300 years than our modern English has changed in 500 years. Homer and Socrates, Plato and Aristotle could sit down at the foot of the Acropolis today and read a Greek newspaper.
A famous scholar by the name of Dr. J. T. Conant wrote a book in which he copied every instance of the use of the word baptizo from 100 B. C. to 1,000 A. D. In every instance that the word has been used in the history of the Greek language, it has never had any other meaning than the simple meaning, to immerse or to dip.