• Webster's Revised Unabridged Dictionary
    • adv Overthwart Across; crosswise; transversely. "Y'clenched overthwart and endelong."
    • prep Overthwart Across; from alde to side of. "Huge trees overthwart one another."
    • Overthwart Crossing in kind or disposition; perverse; adverse; opposing. "Overthwart humor."
    • Overthwart Having a transverse position; placed or situated across; hence, opposite. "Our overthwart neighbors."
    • n Overthwart That which is overthwart; an adverse circumstance; opposition.
    • v. t Overthwart To cross; to oppose.
    • ***
Century Dictionary and Cyclopedia
    • overthwart Athwart; across; crosswise; from side to side.
    • overthwart Exceedingly; excessively.
    • overthwart Across; from side to side of.
    • overthwart On the other side of.
    • overthwart Over against; opposite.
    • overthwart Opposite; situated on the opposite side.
    • overthwart Contrary; cross; perverse; contradictory.
    • n overthwart An adverse or thwarting circumstance.
    • n overthwart Contradiction; quarreling; wrangling.
    • overthwart To cross; pass or lie across.
    • overthwart To thwart; oppose; hinder.
    • ***
Chambers's Twentieth Century Dictionary
    • v.t Overthwart ō-vėr-thwawrt′ to lie athwart: to cross
    • adj Overthwart opposite, transverse: contrary, perverse
    • prep Overthwart across, on the other side of
    • ***


In literature:

But Sir Launcelot rode overthwart and endlong in a wild forest, and held no path but as wild adventure led him.
"Le Morte D'Arthur, Volume II (of II)" by Thomas Malory
The hero goes "overthwart and endlong," just like the figures whom all readers know in Malory, and some in his originals.
"Essays in English Literature, 1780-1860" by George Saintsbury
She hath parted with her velvet gown, embroidered overthwart, to my lady Sand's woman.
"Harper's New Monthly Magazine, Vol. III, No. XVII, October 1851" by Various

In poetry:

Since so ye please to hear me plain,
And that ye do rejoice my smart,
Me list no lenger to remain
To such as be so overthwart.
"Since ye so Please" by Thomas Wyatt