noun

• (UK, dialectal) A bundle of straw laid out straight, chiefly to be used for thatching; a helm.
  "After the leaves had been removed, as many turnips were thrown together as would lie upon a circle four yards in diameter: yealms of wheat-straw were made, similar to such as are used for thatching, but longer, thicker, and formed with less precision: four tall stakes were then driven into the earth, each a yard from the heap, so as to form a square, each side of which would measure six yards. Two courses of yealms were next placed on the earth, so as to enclose the quadrangle indicated by the stakes; […]"

verb

• (transitive) To choose and lay out (straw) straight to be used for animal fodder or thatching; to helm.
  "Horses thrive particularly well upon it [furze], and are exceedingly lively and hearty in their work; but I have usually given it to them mixed with chaff, containing one part hay, and two parts straw, yelmed together, and cut by a chaff-cutter."
• (intransitive) To choose and lay out straw straight to be used for animal fodder or thatching; to helm.
  "[T]wo or three women are busy ‘yelming’—i.e., separating the straw, selecting the longest and laying it level and parallel, damping it with water, and preparing it for the yokes."