I heard this is one of the possible reasons why Grawp's name is grawp. Well first of all we know that he was the runt of the group. His mother dis-owned him because of this and 2nd we know that he doesn't speak English very well. With these 2 facts i've come to the conclusion that Grawp probably stands for "Grow-Up" which is probably what he heard a lot of while he was young... And i'm almost positive that we haven't heard the last from Grawp. (Maybe he marries Umbridge!! LOL)