“罕见的”的英语可以翻译为：infrequent，peculiar，rare，seldom seen，unusual ...

他得了一种罕见的癌症。He contracted a rare form of cancer.一种罕见的小矮马a rare breed of miniature horses四月份就这样炎热是极其罕见的。It's extremely rare for it to be this hot in April....