The definition for foil is "One that enhances or underscores by contrast." Used in a sentence: The sweet cookie was a perfect foil to the sour lemon sorbet.

The definition for onset is "Beginning." Used in a sentence: Crocuses bloom at the onset of spring, sometimes even before the snow melts.

The definition for pretense is "False intention or purpose." Used in a sentence: The jewel thief entered the mansion under the pretense of fixing a leaky faucet.

The definition for redouble is "To make twice as great." Used in a sentence: As the sun began to set, Brittany redoubled her effort to find the necklace she had dropped in the field.

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.