instant vs second

instant and second both are nouns.

Word	Noun	Adjective	Verb	Adverb
instant	Yes	Yes	No	No
second	Yes	Yes	Yes	Yes

As nouns, instant and second are synonyms defined as:

Other synonyms of instant include minute, moment.

As nouns, second is a hypernym of instant; that is, second is a word with a broader meaning than instant:

instant: a very short time (as the time it takes the eye to blink or the heart to beat)
second: an indefinitely short time

Other hypernyms of instant include bit, minute, mo, moment.

instant (noun)	second (noun)
a particular point in time	the fielding position of the player on a baseball team who is stationed near the second of the bases in the infield
a very short time (as the time it takes the eye to blink or the heart to beat)	the gear that has the second lowest forward gear ratio in the gear box of a motor vehicle
	merchandise that has imperfections; usually sold at a reduced price without the brand name
	a speech seconding a motion
	the official attendant of a contestant in a duel or boxing match
	a 60th part of a minute of arc
	following the first in an ordering or series
	1/60 of a minute; the basic unit of time adopted under the Systeme International d'Unites
	an indefinitely short time
	a particular point in time

instant (adjective)	second (adjective)
occurring with no delay	a part or voice or instrument or orchestra section lower in pitch than or subordinate to the first
demanding attention	coming next after the first in position in space or time or degree or magnitude
in or of the present month

instant (verb)	second (verb)
	give support or one's approval to
	transfer an employee to a different, temporary assignment

instant (adverb)	second (adverb)
	in the second place