真的有thrice這個英文字嗎?

是真的。

thrice (adv.) [副詞]
☀ three times, as in succession; on three occasions or in three ways.
☼ 三倍、三次

但的確這是一個比較少用的詞語。

http://hk.dictionary.search.yahoo.com/search?p=thrice

♪ Once 一次
♫ Twice 兩次
♬ Thrice 三次

也參考：
https://hk.knowledge.yahoo.com/question/question;_ylt=A3eg.w9E455TaisAfW7FoolQ?qid=7006052801877

https://hk.knowledge.yahoo.com/question/question;_ylt=A3eg.w9E455TaisAfG7FoolQ?qid=7009073002082

https://answers.yahoo.com/question/index?qid=1006040504959

當然!!!!!!!!!!!!!!!!!!!!!!!!!!!