How to name the diagonals of a square so one can be told from the other?

A square has two diagonals, so how can I to name the separate diagonals if I want to distinguish one from another?

I mean something like the up to down diagonal and the down to up diagonal. Do you have any better suggestions?

• NW-SE and NE-SW. Oct 11, 2015 at 15:01
• George and Martha.
– Drew
Oct 11, 2015 at 20:47

You could borrow a term from heraldry and call them the diagonal dexter and the diagonal sinister. The dexter diagonal would be the one from upper left to lower right, and the sinister diagonal the other one. (In heraldry these things are bends).

• Wow, that's a great answer. I can't upvote, but it definitely deserves it. Other answers are correct too, but they are more like "description"... Oct 12, 2015 at 8:54
• There is one issue that most people are not familiar with these terms, at least in this context. It could work fairly well if defined beforehand but not if dropped in without explanation. Oct 12, 2015 at 9:48

As John Lawler said in the comments, you could use compass points:

NW-SE and NE-SW

If you don't wish to use compass points, another option would be:

bottom-left to top-right and bottom-right to top-left

Of course, in a mathematical context you can label the four corners of the square clockwise as A, B, C, D, and then talk about "the line AC" and "the line BD".