half是啥?

half是啥? 是half hour还是half an hour? half half 是单数还是复数 half是单数还是复数 half past three ,这里half是名词不? half an hour中的half词性为什么是名词? 是a half hours还是a half hour? one half与one-half 是一个意思吗 是one and half hours还是one and half hour? half的用法是 one and a half years 还是one and a half year?half具体的用 是in the half-time 还是on the half-time 还是at 他和half time