Baptism means full immersion i.e. being submerged under the water
So, let us begin by looking at what baptism in water is. The word ‘baptise’ simply means to completely dip something under water, in the same way that you would with a sheep dip. Thus a farmer when dipping his sheep is, in the literal sense of the Greek word, 'baptizing' them. It means to completely submerge them beneath the water.
Strangely, the word 'baptize' is the original Greek word. The reason we use the original Greek word rather than our own English words 'submerge' or 'immerse' is because at the time that the King James Bible was being translated, shortly before 1611, a fierce debate was raging about how baptism should be done.
Some felt that it should be by sprinkling with water on the head and that it should be done to babies. Others argued that it should be done only with those who are old enough to believe and decide to be baptised for themselves, and that it should be done by full immersion in water.
Rather than offend either group the translators of the King James Bible chose simply to use the original Greek word 'baptizein' as a transliteration. They just Anglicised the very Greek word itself, to create the word 'baptise' without translating it at all. Then it was up to every man to give it whatever meaning that he believed it had. That was how the King James translators chose to get themselves out of a very tight corner.
There ought not to be any controversy over what the Greek word 'baptizein' means. Its meaning is totally clear and beyond any doubt. In fact, in 1860 a leading scholar, and Bible translator, Thomas J. Conant (1802 - 1891) was working on the translation of the American Standard Version (and the Revised Standard Version). He argued that we should stop using the words 'baptism' and 'baptise' altogether. Instead he said that we should translate the original Greek words into English (i.e. 'submerge' or 'immerse') just as we do with all the rest of the words in the Bible.
Thus, he wanted to simply translate it as 'submerge' or 'immerse' every time the Greek word 'baptizein' was in the text. That was clearly the right approach but he could not get the committees to accept what he said. It was too controversial for them.
Their reasons for not taking this obviously correct step were presumably the same as with the translators of the King James Bible in 1611. They feared a backlash of criticism from all those people whose denominational tradition was to practise baptism by sprinkling with water. The reason that is done is simply because the person being 'baptised' is only a baby and would not react well to being dipped under the water. So, the error of baptising babies led on, for practical reasons, to the error of sprinkling rather than submerging. It was not done because the Bible says so, because it doesn’t.
So, Thomas Conant left the translation committee and wrote a book called 'The meaning and use of baptizein'. In that book he gives 236 examples of the use of the Greek word 'baptizein' in both the New Testament and secular Greek literature. In fact he chose every instance where the word was ever used in the whole New Testament and in all surviving secular Greek literature.
He found, without any exceptions whatsoever, that it always meant 'submerge' or 'immerse', that is to plunge someone or something entirely under the water. For example it was used to refer to a ship sinking in the sea and so forth. In the whole of Greek literature of any kind there is no other use ever made of that word. Doesn't that settle it? If so, what are we doing sprinkling people's foreheads with water? It is entirely unbiblical. So, for example, the way that we ought to have translated Mark 16:16 would be:
"He who has believed and has been submerged in water shall be saved...."
If we translated 'baptizein' like that, as we ought to, there being no valid reason not to, then it would make the meaning unmistakeable. Instead of this it is being obscured.