lethargic

As an adverb languidly

is in a languid manner, without force or effort, in a manner requiring little energy or exertion.

As an adjective lethargic is

sluggish, slow.

As adjectives the difference between tepid and lethargic

is that tepid is lukewarm; neither warm nor cool while lethargic is sluggish, slow.

As adjectives the difference between stagnant and lethargic

is that stagnant is lacking freshness, motion, flow, progress, or change; stale; motionless; still while lethargic is sluggish, slow.

As a noun languor

is (uncountable) a state of the body or mind caused by exhaustion or disease and characterized by a languid feeling: lassitude.

As an adjective lethargic is

sluggish, slow.

As adjectives the difference between lackluster and lethargic

is that lackluster is lacking brilliance or intelligence while lethargic is sluggish, slow.

As adjectives the difference between lethargic and fatigued

is that lethargic is sluggish, slow while fatigued is tired; weary.

As a verb fatigued is

past tense of fatigue.

As adjectives the difference between lethargic and feeble

is that lethargic is sluggish, slow while feeble is deficient in physical strength; weak; infirm; debilitated.

As a verb feeble is

to make feeble; to enfeeble.

As adjectives the difference between lethargic and soporific

is that lethargic is sluggish, slow while soporific is tending to induce sleep.

As a noun soporific is

something inducing sleep, especially a drug.

As adjectives the difference between lethargic and drained

is that lethargic is sluggish, slow while drained is lacking motivation and energy; very tired; knackered.

As a verb drained is

(drain).

As adjectives the difference between lethargic and paramount

is that lethargic is sluggish, slow while paramount is supreme; highest; chief.