(Incorporating The New Apathesaurus)
Apathy, noun; inaction due to indifference, lack of enthusiasm, lethargy
Detachment, noun; an absence of connection, engagement or interest
Doldrums, noun; a place or period of stagnation, ennui or lassitude
Dullness, noun; the property of being boring, tedious or uninteresting
Ennui, noun; a state of boredom, often induced by tedium and a general sense of pointlessness
Fatigue, noun; tiredness, exhaustion, lethargy, exhaustion, sleepiness
Flatness, noun; a lack of significant or engaging features, a feeling of pointlessness and boredom
Indifference, noun; a lack of interest, engagement, connection, concern or enthusiasm
Lassitude, noun; a condition of weary lethargy
Lethargy, noun; a condition of fatigue, emotional inertia, heaviness or indifference
Listlessness, noun; a lack of energy; weariness and sleepy indolence
Monotony, noun; an absence of variety, the tedium of endless repetition
Pococurantism, noun; indifference, carelessness, lethargic lack of interest
Sameness, noun; a soporific lack of variety; monotony
Taedium Vitae, noun; a state of extreme lethargy, boredom of everything
Tediousness, noun; see Tedium
Tedium, noun; dullness, monotony, boredom, etc.