Definition of "jaum"

But if the Window-Frame stands on a Timber-house, the Head and Ground-sell are sometimes Tennanted into Posts of the Carcass; and then the Posts do the Office of the outer Jaums of the Window-Frame […]

1703, Joseph Moxon, Mechanick Exercises, London: D. Midwinter & T. Leigh, 3rd edition, p. 143

The nineteenth Figure represents the inward and outward Edges of a twisting Schofeet of a Semicircular Door, or Window, whose Jaums, from the Beginning to the Springing Arch, splays more or less, according to the Humour of the Builder, and whose Crown lies level without splaying […]

1725, William Halfpenny: The Art of Sound Building‎, London, page 13