How about *[axis][1]*? 

> 2. (Mathematics) one of two or three reference lines used in coordinate geometry to locate a point in a plane or in space.

(Collins English Dictionary – Complete and Unabridged)

**Update:**

You say you're looking for a name for a code variable. Seeing as people here struggle so much to find such a word, I'm guessing whatever you settle on will confuse whoever reads your code just as much. I'd just skip trying to be pithy and go for `rowOrColumn`. Clarity over brevity.

  [1]: http://www.thefreedictionary.com/axis