1. Because.

2. Not this, but the other.

3. Who or which, relating to an antecedent.

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

• thith,
• tht,
• thrart,
• thathe,
• athet,
• mthat,
• thaugt,
• thad,
• thets,
• what,
• tthat,
• thak,
• thst,
• ethat,
• thatf,
• thwat,
• thetr,
• thatan,
• thwt,
• thatm

• Thad,
• thd,
• thud,
• thoth,
• thweatt,
• Theda,
• theta.

The adjective form of the word "that" is "that".

The plural form of the word "that" is "those"

The singular form of the word "That" is "it"