"查生词" 的英文表达是 "look up new words in a dictionary".
"Look up" 在这里表示查找，"new words" 表示新词汇。由于 "dictionary" 是查找词汇的常用工具，因此在这里直接使用。
例句：
I always look up new words in a dictionary when I come across them in my reading. (我在阅读中遇到新词时总是会在词典中查找。)
She looked up the word "preposterous" in the dictionary because she had never seen it before. (她在词典中查找了"preposterous"这个词，因为她以前从未见过。)