adversary
The definition for adversary is "One who opposes or resists." Used in a sentence: Franklin hoped to defeat his adversary in the afternoon's tennis match.
grandiose
The definition for grandiose is "With an affectation of grandeur." Used in a sentence: The sweeping, grandiose staircase looked preposterous in the modest entry hall.
incisive
The definition for incisive is "Impressively direct and decisive." Used in a sentence: Samir's incisive leadership made him the natural choice for president of the company.
retroactive
The definition for retroactive is "effective as of a prior time or condition." Used in a sentence: The retroactive law made even past infractions punishable.
serenity
The definition for serenity is "Calmness." Used in a sentence: The serenity of the glassy sea soothed the sailors after the big storm.