What is the X in X-mas?
early 15c., "one who keeps watch," from Middle French garde "guardian, warden, keeper; watching, keeping, custody," from Old French garder "to keep, maintain, preserve, protect" (corresponding to Old North French warder, see gu-), from Frankish *wardon, from Proto-Germanic *wardo- "to guard" (see ward (v.)). Abstract or collective sense of "a keeping, a custody" (as in bodyguard) also is from early 15c. Sword-play and fisticuffs sense is from 1590s. Guard-rail attested from 1860.
(1.) Heb. tabbah (properly a "cook," and in a secondary sense "executioner," because this office fell to the lot of the cook in Eastern countries), the bodyguard of the kings of Egypt (Gen. 37:36) and Babylon (2 Kings 25:8; Jer. 40:1; Dan. 2:14). (2.) Heb. rats, properly a "courier," one whose office was to run before the king's chariot (2 Sam. 15:1; 1 Kings 1:5). The couriers were also military guards (1 Sam. 22:17; 2 Kings 10:25). They were probably the same who under David were called Pelethites (1 Kings 14:27; 2 Sam. 15:1). (3.) Heb. mishmereth, one who watches (Neh. 4:22), or a watch-station (7:3; 12:9; Job 7:12). In the New Testament (Mark 6:27) the Authorized Version renders the Greek _spekulator_ by "executioner," earlier English versions by "hangman," the Revised Version by "soldier of his guard." The word properly means a "pikeman" or "halberdier," of whom the bodyguard of kings and princes was composed. In Matt. 27:65, 66; 28:11, the Authorized Version renders the Greek _kustodia_ by "watch," and the Revised Version by "guard," the Roman guard, which consisted of four soldiers, who were relieved every three hours (Acts 12:4). The "captain of the guard" mentioned Acts 28:16 was the commander of the Praetorian troops, whose duty it was to receive and take charge of all prisoners from the provinces.