He thought it was beneath his dignity to talk about his master's decisions and ideas.

beneath 是介词，意思是"在...之下"，在这里引申为"有损于"或"不符合"。 his 是代词 he 的所有格形式，意思是"他的"。 dignity 是名词，意思是"尊严、身份、体面"，指一个人应有的社会地位或自我价值感。 beneath his dignity 这个短语表示"有损他的尊严/身份"，指某件事被认为不符合一个人的社会地位或自我认知。