同志

1. Origins, structure, and basic meaning

• Structure: 同志 (どうし) refers to people sharing an ideal or common activity. 同志が集まる makes them the gathering subject; 同志に手紙を送る makes one the recipient.
• Basic usage: Comrades with the same ideals assemble from many places, while a long-time fellow activist receives a letter.

2. Common pitfalls and similar expressions

• Comrades gathering and a comrade receiving
  • 同志 carries shared conviction or activity more strongly than an ordinary friend. Distinguish the collective subject marked by が from the individual recipient marked by に.