Acedia

Acedia comes from a combination of the negative prefix a- and the Greek noun kēdos, meaning “care, concern, or grief.” (The Greek word akēdeia became acedia in Late Latin, and that spelling was retained in English.)
—Merriam-Webster Dictionary

What the desert fathers meant by acedia does imply a failure of effort, a failure linked to a lack of love—the Greek word they use (a-kedeia) literally means “lack of care.”

Acedia comes from a combination of the negative prefix a- and the Greek noun kēdos, meaning “care, concern, or grief.” (The Greek word akēdeia became acedia in Late Latin, and that spelling was retained in English.)
—Merriam-Webster Dictionary

What the desert fathers meant by acedia does imply a failure of effort, a failure linked to a lack of love—the Greek word they use (a-kedeia) literally means “lack of care.”

“Our struggle is what the Greeks called ἀκηδια [acedia], which we can refer to as a wearied or anxious heart. It is [akin] to sadness and is the peculiar lot of solitaries and a particularly dangerous and frequent foe of those dwelling in the desert.… Once [acedia] has seized possession of a wrecked mind it makes a person horrified at where he is, disgusted with his cell.… He groans quite frequently that spending such time [in his cell] is of no profit to him.…”

The sin which in English is commonly called Sloth, and in Latin, [acedia], is insidious, and assumes such Protean shapes that it is rather difficult to define. It is not merely idleness of mind and laziness of body: it is the whole poisoning of the will which, beginning with indifference and an attitude of “I couldn’t care less,” extends to deliberate refusal of joy culminates in morbid introspection and despair. One form of it which appeals very strongly to some modern minds is the acquiescence in evil and error which readily disguises itself as “Tolerance;” another is that refusal to be moved by the contemplation of the good and beautiful which is known as “Disillusionment,” and sometimes as “knowledge of the world;” yet another is that withdraw into an “ivory tower” of Isolation which is the peculiar temptation of the artist and the contemplative, and is popularly called “Escapism.” The penance assigned to it takes the form of the practice of the opposite virtue: an active Zeal.

—Dorothy Sayers’s commentary on (her translation of) Dante’s Purgatorio, canto XVIII