hoar frost

Noun

hoar frost (countable and uncountable, plural hoar frosts)

1. Originally, any frozen dew forming a white deposit on exposed surfaces.
   • He [the Lord] geueth ſnowe like woll, & ſcatereth yͤ horefroſt like aſhes.1535 October 14 (Gregorian calendar), Myles Coverdale, transl., Biblia: The Byble, […] (Coverdale Bible), [Cologne or Marburg]: [Eucharius Cervicornus and Johannes Soter?], →OCLC, Psalm cxlvij:[16]...
   • [W]hen vve have, as vve very frequently have, put mixtures of ſnovv and ſalt into vials, and left them in the open Air, vve generally obſerv'd, that the outſide of the Glaſs vvas cas'd vvith ice, or covered vvith hoar froſt, directly over againſt that part of the inſide of the Glaſs, vvherein the...1663, Robert Boyle, “Title V. Experiments Touching the Tendency of Cold Upwards or Downwards.”, in New Experiments and Observations Touching Cold, or, An Experimental History of Cold, Begun. […]...

   Synonyms:

   white frost

2. (specifically) Water vapour which has undergone deposition or desublimation (“transformation directly into ice crystals without first turning into liquid water”) when the air is cold and moist to form a white deposit on exposed surfaces.
   • On Sunday night, January 23, ſeveral things vvere laid out at the Obſervatory, ſuch as ſheets of brovvn paper, pieces of boards, plates of metal, glaſſes of ſeveral kinds, &c. vvhich all began to contract hoar-froſt ſeemingly as ſoon as each body had time to cool dovvn to the temperature of the...1780 April 20, Patrick Wilson, “XXVI. An Account of a Most Extraordinary Degree of Cold at Glasgow in January Last; together with Some New Experiments and Observations on the Comparative Temperature...
   • This striking fact, of the lower temperature of the surface on which dew and hoarfrost are forming, it was always found difficult to explain; for the transition of a body from the state of vapour to the fluid or solid form is always accompanied with an evolution of heat, […] The surface is not...1817, John Murray, “Of Caloric”, in Elements of Chemistry. […], 4th edition, volume I, Edinburgh: […] Francis Pillans, […]; London: Longman, Hurst, Rees, Orme, & Brown, →OCLC, book II (Of Repulsion...