mid-12c., pes, "freedom from civil disorder, internal peace of a nation," from Anglo-French pes, Old French pais "peace, reconciliation, silence, permission" (11c., Modern French paix), from Latin pacem (nominative pax) "compact, agreement, treaty of peace, tranquility, absence of war" (source of Provençal patz, Spanish paz, Italian pace), from PIE root *pag- "to fasten" (which is the source also of Latin pacisci "to covenant or agree;" see pact), on the notion of "a binding together" by treaty or agreement.
It replaced Old English frið, also sibb, which also meant "happiness." The modern spelling is from 1500s, reflecting vowel shift. From mid-13c. as "friendly relations between people." The sense of "spiritual peace of the heart, soul or conscience, freedom from disturbance by the passions" (as in peace of mind) is from c. 1200. Sense of "state of quiet or tranquility" is by 1300, as in the meaning "absence or cessation of war or hostility." Specifically as "treaty or agreement made between conflicting parties to refrain from further hostilities," c. 1400.
Used in various greetings from c. 1300, from Biblical Latin pax, Greek eirēnē, which were used by translators to render Hebrew shalom, properly "safety, welfare, prosperity." As a type of hybrid tea rose (developed 1939 in France by François Meilland), so called from 1944.
The Native American peace pipe, supposedly smoked as the accompaniment of a treaty, is recorded by 1760. Peace-officer "civil officer whose duty it is to preserve public peace" is attested from 1714. Peace offering "offering that procures peace or reconciliation, satisfaction offered to an offended person" is from 1530s. Phrase peace with honor dates to 1607 (in "Coriolanus"). The U.S. Peace Corps was set up March 1, 1962. Peace sign, in reference to both the hand gesture and the graphic, is attested from 1968.