主に

1. Origins, structure, and basic meaning

• Structure: 主に (おもに) is an adverb meaning mainly or primarily.
• Basic usage: 主に会議に使われる identifies a room's main use; 主に木を使う identifies a toy maker's primary material.

2. Common pitfalls and similar expressions

• Primary use and primary material
  • The adverb marks the largest share rather than exclusivity; other uses or materials may still exist.