armistice n.

"one of the two times of the year when the sun is at the greatest distance from the equator," mid-13c., from Old French solstice (13c.), from Latin solstitium "point at which the sun seems to stand still," especially the summer solstice, from sol "the sun" (from PIE root *sawel- "the sun") + past participle stem of sistere "stand still, take a stand; to set, place, cause to stand" (from reduplicated form of PIE root *sta- "to stand, make or be firm"). In early use, Englished as sunstead (late Old English sunstede).

The season of the year when the Sun is in the Tropicks, are called the Solstices, because at those times the Sun seems to be at a stand with regard to his declination, neither going further from the Equator, nor coming nearer to it for several days. [Thomas Harrington, "Science Improved," 1774]

[weapon], c. 1300, armes (plural) "weapons of a warrior," from Old French armes (plural), "arms, weapons; war, warfare" (11c.), from Latin arma "weapons" (including armor), literally "tools, implements (of war)," from PIE *ar(ə)mo-, suffixed form of root *ar- "to fit together." The notion seems to be "that which is fitted together." Compare arm (n.1).

The meaning "branch of military service" is from 1798, hence "branch of any organization" (by 1952). The meaning "heraldic insignia" (in coat of arms, etc.) is early 14c., from a use in Old French; originally they were borne on shields of fully armed knights or barons. To be up in arms figuratively is from 1704; to bear arms "do military service" is by 1640s.