periodic

periodic
/ˌpɪərɪˈɔdɪk; ˌpɪrɪ`ɑdɪk/ adj
occurring or appearing at (esp regular) intervals 定期的; 周期的
    periodic attacks of dizziness 眩晕的周期性发作
    a periodic review of expenditure 对支出的定期核查.

牛津英汉双解词典