department       
noun [ C, + sing/pl verb ] uk/dɪˈpɑːt.mənt/ us/dɪˈpɑːrt.mənt/ (written abbreviation dept)
A2 (组织或机构中的)部,系,处,科,室
a part of an organization such as a school, business, or government that deals with a particular area of study or work
  the chemistry department/the department of chemistry 化学系 
 The sales department is/are having a Christmas party this week. 本周销售部将举办圣诞晚会。 
 the Department of Health and Social Security 健康与社会保障部 
 - More examples
 - Please submit your claim for travelling expenses to the accounts department.
 - If this project fails it will affect not only our department, but also the whole organization.
 - Our kitchenware department is in the basement.
 - The art department and the main college are in two separate buildings.
 - He blamed the lack of liaison between the various government departments.
 
Idioms      
be someone's departmentidiom  informal 属于(…的)职责范围内的事,是(…的)份内之事
to be a particular person's area of responsibility
  Wasn't buying the tickets your department, Dan? 丹,你不是负责买票吗? 
 in the brain/looks departmentidiom  humorous 在智力/相貌方面
in intelligence or beauty
  He's somewhat lacking in the brain department. 他的脑子有点儿慢。