An almost imperceptible space of time. See Synonyms at moment.
A particular or precise time: at the instant of combustion.
Abbr. inst. The current month: your letter of the 15th instant.
A food or beverage designed for quick preparation.
adj.
Occurring at once; immediate: instant gratification.
Imperative; urgent: an instant need.
Now under consideration; present.
Commercially prepared or processed for quick and easy final preparation: an instant cake mix.
Readily soluble in water: instant coffee; instant powdered milk.
Appearing, done, or taking place with or as if with maximum quickness and ease: "She had the gift of instant intimacy"(Sylvia Jukes Morris).
adv. At once; instantly.
[Middle English, from Old French, from Latin īnstāns, īnstant-, present, present participle of īnstāre, to approach : in-, on; see in-2 + stāre, to stand; see stā- in Indo-European roots.] in'stant·ness n.
) institute. 
(ĭn'stənt) 