In context|obsolete|lang=en terms the difference between sad and grieve
is that
sad is (obsolete) dignified, serious, grave while
grieve is (obsolete) a governor of a town or province.
As a adjective sad
is (obsolete) sated, having had one's fill; satisfied, weary.
As a noun grieve is
(obsolete) a governor of a town or province.
As a verb grieve is
to cause sorrow or distress to.