beneficial
The definition for beneficial is "Helpful." Used in a sentence: there is no doubt that eating vegetables is beneficial to one's health.
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.
penurious
The definition for penurious is "Extrememly stingy." Used in a sentence: Ebenezer Scrooge was most penurious, refusing to give even a penny to charity.
proximity
The definition for proximity is "Closeness." Used in a sentence: The proximity of Tia's house to school meant that she could walk there in five minutes.
trove
The definition for trove is "Valuable collection." Used in a sentence: Walter's trove of vintage baseball cards was worth thousands of dollars.