2 definitions found for semidiurnal

semidiurnal adjective Date: 1594 1. relating to or accomplished in half a day 2. occurring twice a day 3. occurring approximately every half day <the semidiurnal tides>

Semidiurnal Sem`i*di*ur"nal, a. 1. Pertaining to, or accomplished in, half a day, or twelve hours; occurring twice every day. 2. Pertaining to, or traversed in, six hours, or in half the time between the rising and setting of a heavenly body; as, a semidiurnal arc.