"temporary suspension of hostilities by agreement of the parties," 1707, from French armistice (1680s), coined on the model of Latin solstitium (see solstice), etc., from Latin arma "arms" (see arm (n.2)) + -stitium (used only in compounds), from PIE *ste-ti-, suffixed form of root *sta- "to stand, make or be firm."
The word is attested in English from 1660s in the Latin form armistitium. German Waffenstillstand is a loan-translation from French. Armistice Day (1919) commemorated the end of the Great War of 1914-18 on Nov. 11, 1918, and memorialized the dead in that war. In Britain, after World War II, it merged with Remembrance Day. In U.S. (which suffered fewer casualties and had already a Memorial Day for the dead), Armistice Day became a national holiday in 1926; in 1954, to also honor living World War II and Korean War veterans, it was re-dubbed Veterans Day.