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.

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.