役

1. Origins, structure, and basic meaning

• Structure: 役 (やく) can mean a dramatic part or a real function and duty. Both examples combine 役を with a performance verb.
• Basic usage: 医者の役を演じた is a part in a play; 進める役を担う is the moderator's practical function.

2. Common pitfalls and similar expressions

• Part portrayed on stage and function actually carried out
  • 演じる selects a fictional role, whereas 担う selects an entrusted responsibility. Both are objects, but their semantic domains differ.