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 frugal is "Thrifty, cheap." Used in a sentence: The frugal shopper only bought items that were on sale.

The definition for incongruous is "Not harmonious, incompatible." Used in a sentence: Sadie's cowboy hat was incongruous with her black cocktail dress.

The definition for interminable is "Never ending, or seemingly endless." Used in a sentence: The impatient Zoe found the longwinded lecture interminable.

The definition for rail is "To scold in harsh language." Used in a sentence: Clay began to cry as his irate manager railed at him for missing the deadline.