1. The long giant battering ram from Lord of the Rings: The Return of the King shaped like a giant flaming wolf's head
2. When you get a boner while grinding with a girl at a club, and it presses up against her ass. This term is used because a boner is shaped similar to Grond from Lord of the Rings (long and hard) and also because the word "grond" is similar to "grind"
I gronded a chick last night when we went clubbing and it was like my pants were on fire! It was more awesome than the Battle of Minas Tirith!