1. With that or this.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• therewill,
• hewrewith,
• werewith,
• themwith,
• threwit,
• rherewith,
• fherewith,
• 6herewith,
• 5herewith,
• tgerewith,
• tberewith,
• tnerewith,
• tjerewith,
• tuerewith,
• tyerewith,
• threwith,
• therwith,
• theerwith,
• therweith,
• chairith

• thorite,
• throat,
• thereto,
• throw out,
• Threet,
• three-d.

The adjective form of the word "therewith" is "therewithal".