Basic Guidelines For English Spellings
READ THESE ARTICLES
That is corroborated by an oath; promised or assured by the swearing of an oath; that has sworn an oath. Also: prone to or characterized by oaths of a specified kind or number (only in compounds, as "many-oathed", etc.).
Early 17th century; earliest use found in Thomas Dekker (c1572–1632), playwright and pamphleteer. From oath + -ed.