1) Placed across or lying athwart something else, crosswise.
1417 Thomas Duffeld hafe sextene yerdys over thwart of the garthe fra the wall, York
1500 Item, for a tymmer of putts sewing the overquart semys, jd, York
1517 north and sowth betwixt raynes and the waynway goynge overqwhart it, Threshfield
c.1535 the seyd riotous persons dyd ... cast the seyd dame Anne ouerthwart apon a horse bakk lyke a sekk, Egton
1537 and from thence south overthwart to a close called Carr-rode, Calverley
c.1570 begynyng at the overthwart aley, Almondbury church
1590 Item 4 ouerwhart sykes north and south, Kirby Underdale
1603 the way from the Oldgarth to go overthwart the Colgarthes, Airton
1611 one stone sett overthwarte betwene one house of Nicholas Fenay ... and the groundes there of the said Robert Kay, Almondbury
1643 for the helmewood and props and the overwhart liers [cross-beams], Elmswell
1703 shee falling ill and not able to goe, the Constable took her up and laid her over whart a horse, Hunshelf. As a noun it could mean a lintel: 1537 ij doore cheyks & a fresholde with a overwhart to the same, Bridlington. Used occasionally as a verb: 1573 the accustomed way for cart and carriage which lyeth overthwarting his great new close, Doncaster.