'Semidiurnal' definitions:

Definition of 'Semidiurnal'

From: GCIDE

Semidiurnal \Sem`i*di*ur"nal\, a.
1. Pertaining to, or accomplished in, half a day, or twelve hours; occurring twice every day. [1913 Webster]
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. [1913 Webster]