Is there an adjective for acedia?
Solution 1:
Considering that acedia is described by the NOAD as "spiritual or mental sloth, apathy," I would suggest apathetic, indolent, or lazy.
Solution 2:
I think you are referring to the Capital Sin, Sloth. In such case I'd say slothful. There is also sluggish (it is given as a synonym of listless in the NOAD).
Acedia is the Latin form for "Sloth", in italian "Accidia". (I was able to recognise it for this reason.)