lasting but a moment; very brief; fleeting

a momentary glimpse.

that might occur at any moment; ever impending

to live in fear of momentary annihilation.

effective or recurring at every moment; constant.

adjective

lasting , long-lasting , permanent , staying

adjective

cursory , dreamlike , ephemeral , evanescent , flashing , flitting * , flying , fugacious , fugitive , gone in flash , hasty , impermanent , impulsive , instantaneous , in wink of an eye , like lightning , passing , quick , shifting , short , short-lived , spasmodic , summary , temporary , transient , transitory , vanishing , volatilenotes:momentary means fleeting , brief; momentous means significant and having great consequence , fleet , fleeting , temporal , imminent , impending , proximate , brief , immediate