Synonyms of perpendicular

1 Syllable
sheer, straight, plumb, steep
2 Syllables
steeper, standing, erect, unbent, sheerer, steeping, upright, straightest, stand-up, straight-up, longways, steepest, straighter, plumber
3 Syllables
crosswise, uncurled, collinear, mullioned, sideling, vertical, up-and-down
4 Syllables
vertically, transversely, horizontal, rectilineal, declivitous, precipitous, erectile
5 Syllables
horizontally, contrariwise