The literal meaning of the Greek bapto is to "dip", "dye" (e.g. change color by dipping into a dye) or "immerse" (e.g. John 13.26) whereas the intensive baptiso is used in the NT only in the religious sense. From the Theological Dictionary of the New Testament:
The NT uses βάπτω only in the literal sense, in Lk. 16:24; Jn. 13:26
for “to dip in,” and in Rev. 19:13 for “to dye”; on the other hand it
uses βαπτίζω only in the cultic sense, infrequently of Jewish washings
(Mk. 7:4 K D for ῥαντίσωνται in Lk. 11:38), and otherwise in the
technical sense “to baptise.” This usage shows that baptism is felt to
be something new and strange. The use of → βάπτισμα, βαπτιστής is
Oepke, A. (1964–). βάπτω, βαπτίζω, βαπτισμός, βάπτισμα, βαπτιστής. G. Kittel, G. W. Bromiley, & G. Friedrich (Eds.), Theological dictionary of the New Testament (electronic ed., Vol. 1, p. 530). Grand Rapids, MI: Eerdmans.
In this way, baptism is an initiation into something new, it is transformative and thus symbolizes the death of the old and birth of the new. It is the passing from one life to another.
Israel as a nation was born ("baptized into [the law of] Moses") when it went through the red sea and was engulfed by the cloud, thus symbolic of baptism via water and spirit. Christ baptizes with the holy spirit and with fire, as seen on Pentecost with speaking in tongues and flames above their heads.
Christ's own baptism was crucifixion and death in the grave followed by being raised from the dead and placed at the head of all things by the Father -- another transformation.
In the NT, baptism by fire is symbolic of a trial in which those things that don't last are burned away and the purer parts within are refined and made visible, thus it is again transformative, passing from old to new, with the death of the old and the birth of the new.
Even in secular English usage, if one were to be thrown into a new job in which they had to learn everything on the spot as well as unlearn harmful things, that episode might be referred to as a "baptism of fire" for the new worker, thus this idea has passed even into common English parlance long ago (no doubt from the New Testament).
One of the most eye opening experiences I've had on this site is how the plain meaning of English words seems to have been lost, and I'm not sure whether this is because many don't have English as their native language, or these common words are just being forgotten, but it is a recurring theme. Many of these questions are not even questions about Biblical Hermeneutics, they are questions about the meaning of english words that have been correctly and unambigously translated, but are simply not understood by the reader, and thus a theological dictionary is not needed, a regular dictionary will do to answer the question.