adjective

lasting for a very short time.

fashions are ephemeral: new ones regularly drive out the old

transitory,transient,fleeting,passing,short-lived,momentary,brief,short,cursory,temporary,impermanent,short-term,fading,evanescent,fugitive,fly-by-night,fugacious

noun

an ephemeral plant.

ephemerals avoid the periods of drought as seeds