measure word · a numerical measure word used for poems, songs, and lyrics

他创作了一首非常好听的歌。

numeral, noun, verb · the earliest in time, order, or rank; initial

这是该市首个投入使用的地铁站。

punctuation, noun · the first, the beginning, or the leader of a group.

泰山位列五岳之首，是著名的旅游胜地。

expression, noun, verb · the physical head of a person or animal

昂首挺胸。

verb, noun · the leader, head of an organization, or highest ranking official

他是该组织为首的负责人。