Office: Comes from the Latin officium for duty or task.
My dad, being a deacon in the Catholic church, has to pray the Office (or read the office, or say the office or something like that). This is not the same as watching The Office, but I bet it's equally entertaining. At any rate, Office in that sense is short for Divinum Officium, or "divine duty."
Desk: Comes from discus, as in the thing you throw, which also referred to a plate or platter. The meaning has drifted quite a bit there. Desk job first shows up in 1964, according to the Online Etymology Dictionary. I wonder what they called it before that. Pencil pushers, perhaps, as Dictionary.com tells me that term shows up in the 1880s.
Oddly, according to dictionary.com, desk jockey actually predates desk job by a couple of decades.
I always used to dream of having a job that involved a desk. Having my very own desk, I thought, would mean I'd finally arrived. Well, I'm here. Having a desk is cool and all, but I wouldn't mind not being chained to it. Grass is always greener over the septic tank.
Computer: aka, the thing I spend more time staring at than I do at anything else, even when not forced to. Shows up in the 1600s as "person who computers," shows up in the 1800s for "machine that computes" (did they have machines that computed back then?). A calculator, literally speaking, is a computer. As is an abacus.
Finally, my favorite, pen and pencil. What's neat about these words is that they don't come from the same root at all. Totally unrelated words. Like how koala bears aren't koalas. Kinda. Pen comes from the Latin penna, for feather. I wonder if it's related to penne. Great. Now I want pasta.
Pencil finds its way to us by way of the French word pincel, for a brush used for writing stuff, which is what folks used for writing stuff before pencils existed. Pencil's great, great, great, great grandfather is the Latin word penis, which meant tail or penis. Your pencil's a penis, yo.
Did it just get really boring in here, or is it me?