sacer

Sacer, sacra, sacrum drops its -e- after the masculine nominative, exactly as liber does: sacri, sacro, sacrum, sacris. It marks a thing as made over to a god, and the transfer is the whole point.

That is why the word has a shadow side that English "sacred" has lost. A man declared sacer to a deity was outside human protection and could be killed with impunity, so sacer can mean "accursed" as readily as "holy", and auri sacra fames in Virgil is the "accursed hunger for gold", not the holy one. Keep it apart from sanctus, which is about being protected and morally clean rather than handed over. The neuter plural sacra as a noun means the rites. Family: sacerdos, sacramentum, sacrifico, consecro, sacrilegus (one who steals sacred things). English sacred, sacrifice, sacrament, sacrilege, consecrate.