verb

shine in a bright but brief, sudden, or intermittent way.

lightning flashed overhead

light up,shine,flare,blaze,glare,beam,gleam,glint,sparkle,spark,burn,fluoresce,blink,wink,flicker,shimmer,twinkle,glimmer,glisten,scintillate,glister,coruscate,fulgurate,effulge

noun

a sudden brief burst of bright light.

a flash of lightning

flare,blaze,burst,glare,pulse,blast,gleam,glint,sparkle,flicker,shimmer,twinkle,glimmer,beam,shaft,ray,streak,bar,finger,stream

adjective

ostentatiously stylish or expensive.

a flash new car

ostentatious,showy,bold,flamboyant,conspicuous,obtrusive,extravagant,expensive,pretentious,vulgar,tasteless,in bad/poor taste,tawdry,brash,lurid,garish,loud,gaudy,crude,trashy,flashy,snazzy,nifty,fancy,bling,swanky,jazzy,glitzy,ritzy,tacky,fancy-pants,naff,kitsch,Brummagem