Definify.com
Webster 1913 Edition
Semidiurnal
Semˊi-di-ur′nal
,Adj.
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