A secondary, but still important meaning of this word is that of "identification" or "to be brought into connection or union with someone". For instance, in 1 Corinthians 10:1-3 we read of the people of Israel being "baptized into Moses, in the cloud and in the sea". Now we know that the people cross the Red Sea on dry ground, and that the "cloud" was the pillar of cloud that led them - being God Himself. Many of those who oppose believer's baptism by immersion will cite this text, however the secondary meaning of "brought into connection or union" aids us in making sense of the meaning here. As always, context is the chief aid in determining the dictionary meaning of the word.
What we would advocate is that in all instances where the practice of New Testament water Baptism occurs, the primary mode of "immersion" fits the context of those passages.