The definition for combustion is "Act of burning." Used in a sentence: Campers must use fire with great caution to prevent combustion of the parched brush.

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 placebo is "An inactive substance used in medical testing." Used in a sentence: Tom, who had taken the placebo, found that his allergy symptoms did not go away.

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 regale is "To amuse." Used in a sentence: My clever brother Jeffrey regaled the dinner guests with tales of his adventures.