rarer

1.The rarer it is, the more it is worth.

物以稀为贵。

2.Lines composed primarily of anapestic feet, often with an additional unstressed syllable the end of the first line, are much rarer in English verse.

各基本由仄仄平音步所组成，第一经常附加一非重读音节，英语文，罕见这种诗。