1. Learning.

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

• lanters,
• lettert,
• letere,
• metters,
• lesters,
• lettesr,
• lletter,
• letteuse,
• letetrs,
• leders,
• lecturs,
• lettes,
• lettrer,
• lettet,
• latterws,
• lewtter,
• lters,
• lettec,
• lettters,
• letterto

• betters,
• leadership,
• lettercard,
• leathers,
• Leatrice,
• leaders,
• lederhosen,
• loiters,
• letter.

The adjective form of the word "letters" is "lettered".