incidental

Compared meaning: not very important; less central than the main thing (adjective).

比较义项：次要的，不那么重要的（形容词）。

• secondary

  Ranks something after the most important one; often contrasted with the primary thing, used for skills, roles, concerns and effects; neutral and very common in speech and writing.

  表示某事物的重要性排在最重要的事物之后，常与首要的事物相对，用于技能、角色、关注点和影响等方面；语气中性，口语和书面语都很常用。

  Money matters to her, but job satisfaction always comes first; salary is secondary.

  钱对她来说很重要，但工作满意度总是排在第一位；薪水是次要的。

• peripheral

  Describes something on the margin of the main matter, related but not central to it; often used for people's involvement, issues or details that stay in the background.

  表示某事物处于主要事情的边缘，与之相关但并非核心；常用于形容人的参与程度、议题或细节仍停留在次要位置。

  His involvement in the project was peripheral; he attended only two meetings.

  他在这个项目中的参与只是边缘性的；他只参加了两次会议。

• incidental 本词

  Describes something that arises as a minor, unplanned side effect of something else, especially costs or expenses; emphasizes it was not the main purpose or plan.

  表示某事物是作为另一件事的次要、非计划的附带结果而产生的，尤其常用于费用或开支；强调这并非主要目的或计划。

  Any incidental expenses, like parking or snacks, will be reimbursed by the company.

  任何附带费用，比如停车费或零食费，公司都会报销。

Secondary, peripheral, and incidental can all describe something not very important. Secondary means ranked below the main thing, neutral and common. Peripheral means on the edge of an issue, not central. Incidental means a small, unplanned side effect. Not compared: peripheral (eyesight), secondary (school).

这三个词都能形容不那么重要的事物，但侧重点不同：secondary 强调按重要性排在第二位，语气中性、使用范围广；peripheral 强调处于核心问题的边缘、关联不深；incidental 强调是伴随主要事情而产生的附带结果，常与费用、开支搭配。这里不比较 peripheral 表示外围、周边的字面意义（如 peripheral vision 余光），也不比较 secondary 表示中学的用法（如 secondary school）。