flash vs lightning

flash and lightning both are nouns.

Word	Noun	Adjective	Verb	Adverb
flash	Yes	Yes	Yes	No
lightning	Yes	No	No	No

As nouns, lightning is a hyponym of flash; that is, lightning is a word with a more specific, narrower meaning than flash:

flash: a sudden intense burst of radiant energy
lightning: the flash of light that accompanies an electric discharge in the atmosphere (or something resembling such a flash); can scintillate for a second or more

Other hyponyms of flash include flicker, glint, spark, gleam, gleaming, glimmer, coruscation, glitter, sparkle, heat flash, streak.

flash (noun)	lightning (noun)
a lamp for providing momentary light to take a photograph	the flash of light that accompanies an electric discharge in the atmosphere (or something resembling such a flash); can scintillate for a second or more
a bright patch of color used for decoration or identification	abrupt electric discharge from cloud to cloud or from cloud to earth accompanied by the emission of light
a momentary brightness
a sudden brilliant understanding
a short news announcement concerning some on-going news story
a burst of light used to communicate or illuminate
a gaudy outward display
a sudden intense burst of radiant energy
a short vivid experience
a very short time (as the time it takes the eye to blink or the heart to beat)

flash (adjective)	lightning (adjective)
tastelessly showy

flash (verb)	lightning (verb)
appear briefly
emit a brief burst of light
make known or cause to appear with great speed
protect by covering with a thin sheet of metal
run or move very quickly or hastily
gleam or glow intermittently
display proudly; act ostentatiously or pretentiously
expose or show briefly