Definition of "yron"

The seven-fold yron gates of grislie Hell, And horrid house of sad Proserpina, They able are with power of mightie spell To breake, and thence the soules to bring awaie Out of dread darkenesse to eternall day, And them immortall make which els would die In foule forgetfulnesse, and nameles lie.

1591, Edmund Spenser, The Poetical Works of Edmund Spenser, Volume 5‎

And I went on bourd into one of them, wherein I could not finde any yron at all […] .

1600, Richard Hakluyt, The Principal Navigations, Voyages, Traffiques and Discoueries of the English Nation‎