arriswise

from The Century Dictionary.

• Diagonally: said of an arrangement of tiles or slates so that one angle points downward.
• In heraldry, with one angle projecting toward the spectator: said of any bearing of a rectangular form so placed that one corner is in front, and the top and two of the sides are shown. Erroneously written arraswise.

from the GNU version of the Collaborative International Dictionary of English.

• adverb Diagonally laid, as tiles; ridgewise.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adverb Diagonally, as timber so sawn (lengthwise) or tiles so laid relative to walls or a way.