1) Mixed grain, especially rye mixed with wheat. It could refer to the mixed flour or the crop in the fields.
1578 Item musselgeom one bushell, Stockeld
1612 2 bushells of maslen whereof 5 peckes was rye and 3 peckes wheat blended, Brandsby
1637 one bushel of Maslin, Knaresborough
1642 lands wheare wee intende to sowe either Rye or Massledine, Elmswell
1698 a sheaf of masleion … covered with gleanes, West Riding
1710 bought a stroak of masslejen
1721 six stroakes of misling meal in a kimlin, Fewston
1729 a peck of misslegen, Saxton
1758-62 There is a sort of coarse flower att Wakefeild to be bought that is called measlin wich makes good loaf bread and is healthful bread. Mashonger is wheat and rye ground together 1798 Shearing wheat and maslin in Lodge Field, Sessay Park. In the first reference quoted it was contrasted with cleane wheat. It developed a number of different spellings, some of them erratic.
2) A type of brass, or a vessel made of this metal.
1434 unum brassepott, majorem patellam de meslyn, Campsall
1481 ‘one basin de Masselyn’, Thornhill
1506 a basyne and oon ewere of myslyne, York
1511 j pelvim, j lavacrum le maslyn’, Beckwithshaw
1555 ij messilling bassens, Kendal
1560 one masleyne panne, Almondbury
1573 'a myslyne basyn worth 5s', Acomb.