[ygolo]

Oh. A lot of the names come about for historical reasons.
The enhancement MOSFET was not the first field effect transistor(FET), nor was a FET the first transistor. Bipolar Junction Transistors (BJTs) were first. Before that there were vacuum-tubes.

BJTs useful terminals were the emitter, collector and base (which made some sense based on the physical flow of charge carriers, but I wouldn't be surprised if they were left over from the vacuum-tube days). I think source and drain were to make them sound like emitter and collector. In an enhancement MOSFET, source and drain are physically the same due to the symmetry of the structure. You may be able to think of it like the charge carriers starting from the source and "draining" into the drain, but that is not really accurate. The gate you can think of as "gating" the transistor operation. Open the "gate" to have the current flow? The "bulk" may be an allusion to the fact that we have "bulk" silicon before any of the processing is done to make it an integrated circuit.

I'm speculating. I've gotten so used to calling them what they are conventionally called, I am not sure I can give accurate answers.

With this stuff, (and probably a lot of EE/CS related things) the naming tends to be highly arbitrary and based on the history of development. IMO, it is better to learn the meaning of terms through their use and context, since they often have little intrinsic value to their name.

The names are often just labels. That's my opinion. But I haven't really been tripped up by not knowing the etymology of technical terms. Why is the mouse called a "mouse" (perhaps it resembles one)? Why are errors in design or construction called "bugs?" (a hold-over from the vacuum-tube days?). There probably are reasons for the names, but many times they are lost to history.