Circle Backslash ⍉

Monadic Circle Backslash means Transpose

      mat
1 2 3
4 5 6

      ⍉ mat
1 4
2 5
3 6

Dyadic Circle Backslash means Dyadic Transpose

      2 1 ⍉ mat
1 4
2 5
3 6
      1 1 ⍉ mat     ⍝ leading diagonal
1 5