WordNet sense 1 (worthy of notice):

noteworthy, remarkable

WordNet sense 2 (fairly large or important in effect; influential):

large

WordNet sense 3 (of very great significance):

momentous

WordNet sense 4 (important in effect or meaning):

significant

WordNet sense 5 (having authority or ascendancy or influence):

authoritative

WordNet sense 6 (having or exercising influence or power):

influential

WordNet sense 7 (having or showing an exaggerated opinion of your importance, ability, etc):

immodest

WordNet sense 8 (of great consequence):

serious

WordNet sense 9 (of major significance or importance):

great

WordNet sense 10 (of great gravity or crucial import; requiring serious thought):

heavy, weighty, grave

WordNet sense 11 (the most important and magnificent in adornment):

grand

WordNet sense 12 ((used of persons) standing above others in character or attainment or reputation):

distinguished

WordNet sense 13 (having important issues or results):

consequential, eventful

WordNet sense 14 (most important element):

chief, primary, principal

WordNet sense 15 (significant):

big

WordNet sense 16 (of the greatest importance):

crucial, essential

WordNet sense 17 (of great significance or value):

of import

WordNet sense 18 (forming or having the nature of a turning point or crisis):

critical, decisive