Va'Eira I: Exactly What Is A Tanin?

The Torah describes how the staff that Aharon threw down on the ground turned into a tanin. What exactly is a tanin? The truth is that growing up I was always taught that it was a snake. This is how Rashi (7:10) defines it. However, one could ask that if it is a snake why does the Torah use the term tanin and not “nachash”, especially since in Parshas Shemos the Torah uses the term “nachash”. The Sifsei Chachamim seems to answer this question by saying that a nachash is a snake found on dry land and a tanin is found in the water. Presumably, what he means is that when Moshe was in the desert, the stick turned into a “nachash”, but now that Moshe is in Mitzryim which is near the Nile, it turned into a tanin. (The Da’as Mikra has a similar p’shat).
However, there is another p’shat given to the word “tanin”. Rav Hirsch translates it as a crocodile. This p’shat is based on a pasuk in Yechezkel (25:28) which is the Haftorah for Parshas Va’Eira. The posuk compares Pharoah to the “tanin hagodal” found in the water. Rav Hirsch understands this to be referring to a crocodile. This p’shat also fits in very well with a Malbim I alluded to at the end of my earlier post. The Malbim writes that the chartumei Mitzrayim were a bunch of charlatans who were very good at deceiving the people. In order to replicate what Aharon did , some of the chartumim brought out taninim skins and hid under them. When some of the chartumim threw down their sticks, the other chartumim jumped out hidden under the taninim skins and crawled around. People thought the sticks (which were also now hidden under the skins) had turned into taninim. The Malbim adds that later when Aharon’s stick swallowed the other sticks, it also swallowed the people under the taninim skins. The malbim’s pshat is more understandable if you assume a tanin is a crocodile as opposed to a snake.