The Collaborative International Dictionary
Sacro-
Sacro- \Sa"cro-\ (Anat.) A combining form denoting connection with, or relation to, the sacrum, as in sacro-coccygeal, sacro-iliac, sacrosciatic.
Douglas Harper's Etymology Dictionary
sacro-
word-forming element meaning "of or involving the sacrum, the bone at the base of the spine. E.g. sacro-iliac.
Wiktionary
sacro-
pre. Of or relating to the sacrum.