Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.
SADD
As described in historical dictionaries
Patronymica Britannica (1860)
SADD. O. Eng. sadde; not s.ad, wretched, in the modern sense, but grave, serious. Two centuries ago any thing dull or heavy was so called, as sad colour, sad bread, &c.