a.[Z][B]

1. 周期的，周期性的；定期的
   the periodic motion of a planet

   行星的周期运动

2. 时而发生的；间歇（性）的
3. 【数】循环的；周期函数的
4. 【语】完整句的

adj.

1. appearing or occurring at intervals.
2. Chemistry  relating to the periodic table of the elements or the pattern of chemical properties which underlies it.
3. relating to a rhetorical period.