This is the 1834th most frequent Chinese word.
郑
"郑" (Zhèng) is a Chinese surname and can also refer to an ancient state in Chinese history.
In this sentence, "郑" is used as a surname, referring to the person 'Mr. Zheng'
郑先生是一位优秀的工程师。
Mr. Zheng is an excellent engineer.
Here, "郑" is part of the compound word "郑重", which means solemn or serious, describing the manner of declaration.
为了表达自己的真心，他郑重声明。
To express his sincerity, he solemnly declared.
In this sentence, "郑" is part of a place name '郑州', referring to the city Zhengzhou.