not reliable or responsible, esp. in business; untrustworthy

a fly-by-night operation.

not lasting; brief; impermanent; transitory

a fly-by-night theater.

a person or thing that is unreliable, esp. a debtor who evades or attempts to evade creditors.

a person regarded as a poor credit risk.

adjective

dependable , reliable , reputable , responsible , trustworthy

adjective

brief , cowboy * , disreputable , dubious , ephemeral , evanescent , fleeting , here-today-gone-tomorrow , impermanent , irresponsible , momentary , not to be relied upon , not to be trusted , passing , questionable , shady , shifty , short-lived , slimy * , slippery * , temporary , treacherous , trustless , undependable , unprofessional , unreliable , unsure , untrustworthy , unscrupulous