“坚持背单词”可以用英文表达为 "to persist in memorizing vocabulary"，它来源于动词 "persist" 和 "memorize"。
"persist" 意思是坚持，坚决，而 "memorize" 意思是记忆。
例句：
I need to persist in memorizing vocabulary if I want to improve my Engpsh. (我需要坚持背单词才能提高我的英语水平。)
He persisted in memorizing vocabulary for an hour every day. (他每天坚持背单词一小时。)
Persist in memorizing vocabulary, and you'll see improvement in your language skills. (坚持背单词，你会发现你的语言技能有所提高。)