1. 含义为“处于较高层次，具有高级属性；年龄较大；在等级或职位上更为优越”。(形容词形式)
常用组合形式
senior high( school ) 初级中学
senior citizen 高龄公民（一种委婉的称谓，通常指已退休的群体）
be senior to sb. 在年龄上超越某人；在职位上高于某人
例如：
*(2019.江苏) In order to experience the ease brought by digital transactions, a significant number of senior citizens have begun utilizing smartphones.为了体验数字交易的便捷性，众多高龄公民开始使用智能手机。
I have accumulated ten years of professional experience in senior management positions.我在高层管理岗位上有十年的工作经验。
My brother Bob surpasses me in age by two years.我哥哥鲍勃比我年长两岁。
He is also an educator, yet holds a higher position than me.他同样是一名教育工作者，但职位级别在我之上。
2. 含义为“年龄上更长者；等级或职位上更优越者，上级；中学阶段的学生”(名词形式)[C ]例如：
It is considered discourteous for children to interrupt their seniors while they are engaged in conversation.当长辈们交谈时，孩子们插嘴被认为是不礼貌的行为。
Lily is known for her vivacity and diligence, and has been commended by her seniors in the corporate environment.丽丽以其活泼和勤奋而著称，并在企业环境中获得了上级的赞扬。
特别提示
senior这个词本身就蕴含了比较的意味，因此它没有比较级和最高级的变化形式。在表达比较关系时，其后应使用介词to而非than。