This is a very late reply to itkatch:
Sorry I took so long to get back--I didn't really write down the exact error I got when accessing the Wikipedia file from a usb drive using Aardict. In the meantime, I reflashed my n810 and it has taken me over a week to get almost everything installed that I wanted in place.

What I finally did was move the third (and smallest) part of the Wikipedia for Aardict onto my 8 GB micro SD card (which is what I boot off of). The short of it: it now works.

I suspect that the problem was with my USB connection and not the Wikipedia file. In the future, if I face this problem again with the SD card, I might try transferring the 2+ GB files over via ftp.

As far as transferring over via a USB flash drive/n810 in USB host mode: Whenever I transfer files of any size (i.e., > 1 MB), the transfer fails. I suspect that it's because my Patriot Xporter 32 GB drive needs extra power for larger transfers and the micro USB port on the n810 is not up to the task, power-wise.