Synonyms of diagonally

2 Syllables
aslant, slantways, slaunchways, askew, longways
3 Syllables
slantingways, slantwise, crosswise, mullioned
4 Syllables
vertically, cater-corner, catty-corner, cornerwise, kitty-corner, transversely, kittycorner, catercorner, obliquely, cattycorner
5 Syllables
horizontally, contrariwise