a.[Z][B]

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

   行星的週期運動

2. 時而發生的；間歇（性）的
3. 【數】循環的；週期函數的
4. 【語】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.