From The Collaborative International Dictionary of English v.0.48 :
Aslope \A*slope"\, adv. & a. [Pref. a- + slope.]
Slopingly; aslant; declining from an upright direction;
sloping. "Set them not upright, but aslope." --Bacon.
[1913 Webster]
From WordNet (r) 3.0 (2006) :
aslope
adj 1: having an oblique or slanted direction [syn: aslant,
aslope, diagonal, slanted, slanting, sloped,
sloping]