gargantuan
The definition for gargantuan is "Gigantic." Used in a sentence: The gargantuan monster towered over the ten–story bulding.
gravity
The definition for gravity is "Importance, significance." Used in a sentence: Understanding the gravity of his error, Ken offered his humblest apology.
incumbent
The definition for incumbent is "Necessary as a duty or responsibility." Used in a sentence: It was incumbent on Jack to attend his father's retirement party.
methodical
The definition for methodical is "Performed in an orderly manner." Used in a sentence: Oscar's methodical approach exasperated his free–spirited friend Ben.
unscrupulous
The definition for unscrupulous is "Lacking principles." Used in a sentence: The unscrupulous salesman was fired for lying to his customers.