The dirk (a knife) appears early on in Charlotte's voyage, and is given to her by Zachariah (2.93). When she first encounters the weapon, she's "horrified" (2.93); however, she gradually learns to wield the weapon. The knife can be used for good [as when she cuts Zachariah free (21.80)] or it can be used for evil [as when Mr. Hollybrass gets stabbed by Captain Jaggery (15.56)]. Also, no snickering please, but the knife is most definitely a phallic symbol. That is, the knife is a symbol of masculine authority that the gender bending Charlotte must learn to use.