What's the "een" in Halloween?
late 14c., past participle adjective from obsolete verb sacren "to make holy" (c.1200), from Old French sacrer "consecrate, anoint, dedicate" (12c.) or directly from Latin sacrare "to make sacred, consecrate; hold sacred; immortalize; set apart, dedicate," from sacer (genitive sacri) "sacred, dedicated, holy, accursed," from Old Latin saceres, from PIE root *sak- "to sanctify." Buck groups it with Oscan sakrim, Umbrian sacra and calls it "a distinctive Italic group, without any clear outside connections." Related: Sacredness.
Nasalized form is sancire "make sacred, confirm, ratify, ordain." Sacred cow "object of Hindu veneration," is from 1891; figurative sense of "one who must not be criticized" is first recorded 1910, reflecting Western views of Hinduism. Sacred Heart "the heart of Jesus as an object of religious veneration" is from 1765.
Reserved for exclusive use by something. The term might mean only writable by whatever it is sacred to.
For example, "Register 7 is sacred to the interrupt handler" would mean that if any other code changed the contents of register 7, dire consequences would ensue.
the power, being, or realm understood by religious persons to be at the core of existence and to have a transformative effect on their lives and destinies. Other terms, such as holy, divine, transcendent, ultimate being (or reality), mystery, and perfection (or purity) have been used for this domain. "Sacred" is also an important technical term in the scholarly study and interpretation of religions