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 ethical is "Conforming to accepted standards." Used in a sentence: Mary did the ethical thing and turned in the diamond necklace she found.

The definition for inauspicious is "Not favorable." Used in a sentence: Gary believed the black foreboding sky was an inauspicious sign.

The definition for incidental is "Minor." Used in a sentence: The accountant advised Justine not to report her incidental expenses.

The definition for stifle is "To repress or discourage." Used in a sentence: Amy tried ineffectively to stifle her giggles after she read Susan's note in class.