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 extant is "Currently existing." Used in a sentence: Some consider Clint Eastwood the greatest extant American director.

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 salvage is "To save from ruin." Used in a sentence: After the fire, Mrs. Han tried to salvage her family photos from the wreckage.

The definition for trove is "Valuable collection." Used in a sentence: Walter's trove of vintage baseball cards was worth thousands of dollars.