The definition for opportune is "Suitable or convenient." Used in a sentence: Quan stepped onto the platform at the most opportune time, just as the train pulled in. The definition for interminable is "never ending, or seemingly endless.", the definition for methodical is "Performed in an orderly manner.", and the definition for placebo is "An inactive substance used in medical testing."

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. The definition for compulsion is "an irresistible impulse.", the definition for condone is "To treat as acceptable.", and the definition for procrastinate is "To put off intentionally."

The definition for diffident is "Lacking self–confidence." Used in a sentence: The diffident student never raised her hand in class, even when she knew the answer. The definition for rehash is "to discuss again.", the definition for ethical is "Conforming to accepted standards.", and the definition for stealth is "The act of moving secretly or unnoticed."

The definition for refurbish is "To brighten or freshen." Used in a sentence: Leeanne cleaned and mended all weekend to refurbish the shabby apartment. The definition for serenity is "calmness.", the definition for heinous is "Shockingly evil.", and the definition for salvage is "To save from ruin."

The definition for negate is "To make invalid." Used in a sentence: Paula negated Tiffany's argument by proving that her main premise was false. The definition for cunning is "showing clever insight.", the definition for obnoxious is "Highly offensive.", and the definition for scamper is "To run quickly."