Boon adjectives are listed in this post. Each word below can often be found in front of the noun boon in the same sentence. This reference page can help answer the question what are some adjectives commonly used for describing BOON.
already, best, better, blessed, common, coveted, dearest, desired, doubtful, economic
enormous, first, for, glorious, gracious, great, greater, greatest, heavenly, highest
huge, immense, incalculable, inestimable, invaluable, last, little, major, mighty, old
only, other, perfect, poor, potential, precious, priceless, proffered, promised, real
rich, richest, same, second, simple, single, small, sordid, special, substantial
such, sweet, tremendous, unexpected, unspeakable, valuable, welcome
Hope this word list had the adjective used with boon you were looking for. Additional describing words / adjectives that describe / adjectives of various nouns can be found in the other pages on this website.