What is the X in X-mas?
Old English style, from West Germanic adjective *stakhlijan "made of steel" (cf. Old Saxon stehli, Old Norse, Middle Low German stal, Danish staal, Swedish stål, Middle Dutch stael, Dutch staal, Old High German stahal, German Stahl), related to *stakhla "standing fast," from PIE *stek-lo-, from root *stak- "to stand, place, be firm" (see stay (n.1)). No corresponding word exists outside Germanic except those likely borrowed from Germanic languages. Steel wool is attested from 1896.
"make hard or strong like steel," 1580s, figurative, from steel (n.). Related: Steeled; steeling.
The "bow of steel" in (A.V.) 2 Sam. 22:35; Job 20:24; Ps. 18:34 is in the Revised Version "bow of brass" (Heb. kesheth-nehushah). In Jer. 15:12 the same word is used, and is also rendered in the Revised Version "brass." But more correctly it is copper (q.v.), as brass in the ordinary sense of the word (an alloy of copper and zinc) was not known to the ancients.