— Copernican
— all important
— all-important
— alpha
— beta
— big
— burning
— cardinal
— central
— chief
— consequential
— crucial
— distinguished
— essential
— eventful
— fundamental
— grand
— grave
— great
— grievous
— heavy
— historic
— important
— in-chief
— key
— main
— master
— measurable
— most-valuable
— of the essence
— outstanding
— primal
— primary
— principal
— serious
— significant
— strategic
— valuable
— weighty