Instant adjectives are listed in this post. Each word below can often be found in front of the noun instant in the same sentence. This reference page can help answer the question what are some adjectives commonly used for describing INSTANT.
awful, breathless, brief, briefest, certain, chaque, critical, eternal, exact
fatal, fifth, final, first, fleeting, fourth, frozen, happy, initial
last, little, long, mere, more, most, next, nth, other
particular, possible, precise, present, previous, proper, right, same, second
seventh, short, single, sixth, specific, split, such, swift, tenth
terrible, third, un, very, wild
Hope this word list had the adjective used with instant you were looking for. Additional describing words / adjectives that describe / adjectives of various nouns can be found in the other pages on this website.