My DD does this too - I think it has to do with her super high verbal abilities and the high level audio books she listens to. The words are always used correctly, just not what you would expect from a second grader. For example every year she does a lemonade stand for charity so we were at DH's campus selling lemonade during a softball game. A student ran back to his dorm room to grab some money but told her that he was buying 2 cups - one for himself and one for his friend. When he came back to pay her DD said "Oh your companion already got his."
Not "friend". Not "the other guy". "Companion". A perfectly appropriate word but not what most kids her age would have used. Probably not what most adults would have used either. She also would say "damaged her finger" but not sure about the "fetch some cars."
Ironically there was a big fuss at school last week because she was asked to make a sentence for the word "pay" and she "couldn't think of an appropriate second to third grade level sentence" for it. She'll give you a sentence for "reimburse" or "expertise" but they were making a fuss over her not giving them a sentence for "pay". Sometimes the quirky giftedness just comes out of left field...
