undertaking

Compared meaning: a planned, large piece of work or task (noun).

比较义项：计划中的大型工作或任务（名词）。

• project

  Neutral, everyday word for any planned piece of work with a clear purpose or deliverable; used for tasks of any size, from a school assignment to a company plan.

  中性、常用的词，指任何有明确目的或成果的计划性工作；大小任务都能用，小到学校作业，大到公司计划。

  The science fair project took him three whole weekends to finish.

  那个科学展览项目花了他整整三个周末才完成。

• undertaking 本词

  Formal, somewhat literary word stressing the scale, effort or seriousness of a task; often paired with 'massive' or 'no small', rarely used for minor everyday tasks.

  较为正式、略带书面色彩的词，强调任务的规模、难度或严肃性；常与“massive”或“no small”搭配使用，很少用来指日常小事。

  Organizing the whole conference alone was no small undertaking.

  独自一人筹办整场会议绝非易事。

Both words mean planned work with a purpose. Project is neutral and common, used for tasks of any size. Undertaking is more formal and literary, stressing size or seriousness of the task. Undertaking can also mean a formal promise; that meaning is not compared here.

这两个词都能指有目的、经过规划的工作，但语气和正式程度不同：undertaking 更书面、更强调任务的规模和分量，project 则是中性常用词，大小任务都能用。这里不比较 undertaking 表示“正式承诺”的意思。