Old English isærn (with Middle English rhotacism of -s-) "the metal iron; an iron weapon," from Proto-Germanic *isarnan (cf. Old Saxon isarn, Old Norse isarn, Middle Dutch iser, Old High German isarn, German Eisen) "holy metal" or "strong metal" (in contrast to softer bronze) probably an early borrowing of Celt. *isarnon (cf. Old Irish iarn, Welsh haiarn), from PIE *is-(e)ro- "powerful, holy," from PIE *eis "strong" (cf. Sanskrit isirah "vigorous, strong," Greek ieros "strong").
Chemical symbol Fe is from the Latin word for the metal, ferrum (see ferro-). Meaning "metal device used to press or smooth clothes" is from 1610s. The adjective is Old English iren, isern. To have (too) many irons in the fire "to be doing too much at once" is from 1540s. Iron lung "artificial respiration tank" is from 1932.