Difference between 'under', 'underneath' and 'beneath'

There really is no difference, but an English speaker might choose between them based on context. It's hard to think of examples right of the top of my head, though. It is true, though, that beneath is often used figuratively. So, for example, i might say: "She was trying to be insulting with her petty remarks about our house, but i didn't respond--it was beneath my dignity to give her the safisfaction of a response." There are also stock phrases in which one or the other of these words might be used. So, for example, when one is pressured to meet a deadline, one might say: "I can't go out tonight, i'm under the gun to get this project done by Monday." The stock phrase "under the gun" means subject to pressure.