adversary
The definition for adversary is "One who opposes or resists." Used in a sentence: Franklin hoped to defeat his adversary in the afternoon's tennis match.
catastrophic
The definition for catastrophic is "Relating to extreme misfortune." Used in a sentence: The effects of the massive hurricane were catastrophic.
dubious
The definition for dubious is "Questionable." Used in a sentence: Karl found Kevin's claim that he was sick dubious, as he had just seen him playing football.
insolence
The definition for insolence is "Boldness or rudeness." Used in a sentence: The boy's insolence to the policeman embarrassed his mother.
moderate
The definition for moderate is "Tending toward the average." Used in a sentence: The best–selling writer was disappointed; his new novel was only a moderate success.