The definition for brandish is "To shake or wave menacingly." Used in a sentence: The baseball player was fined for brandishing his bat at the opposing pitcher.

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 gruff is "Rough or stern in manner or speech." Used in a sentence: Heidi's grandfather was gruff, barking stern orders and hardly smiling.

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.