lackluster

As a verb slump

is (lb) to collapse heavily or helplessly.

As a noun slump

is a heavy or helpless collapse; a slouching or drooping posture; a period of poor activity or performance, especially an extended period.

As an adjective lackluster is

lacking brilliance or intelligence.

As adjectives the difference between torpid and lackluster

is that torpid is unmoving, dormant or hibernating while lackluster is lacking brilliance or intelligence.

As adjectives the difference between crestfallen and lackluster

is that crestfallen is sad because of a recent disappointment while lackluster is lacking brilliance or intelligence.

As adjectives the difference between lackluster and lusterless

is that lackluster is lacking brilliance or intelligence while lusterless is without luster, dull, not shiny, flat or matte finished.

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 lackluster and dark

is that lackluster is lacking brilliance or intelligence while dark is having an absolute or (more often) relative lack of light.

As a noun dark is

a complete or (more often) partial absence of light.

As a noun spiffy

is a spring-wire collar stay, worn by men.

As an adjective lackluster is

lacking brilliance or intelligence.

As adjectives the difference between lackluster and barbaric

is that lackluster is lacking brilliance or intelligence while barbaric is of or relating to a barbarian; uncivilised, uncultured or uncouth.

As adjectives the difference between lackluster and listless

is that lackluster is lacking brilliance or intelligence while listless is lacking energy, enthusiasm, or liveliness.

As adjectives the difference between gloomy and lackluster

is that gloomy is imperfectly illuminated; dismal through obscurity or darkness; dusky; dim; clouded while lackluster is lacking brilliance or intelligence.