from robust + -ous;
In common use during the 17th century.
In the 18th it becomes rare, and is described by Johnson (1755) as ‘now only used in low language, and in a sense of contempt’.
During the 19th it has been considerably revived, especially by archaizing writers.
a 1548 - Chronicle (The Union of the Two Noble and Illustre Famelies of Lancestre and Yorke), Edward Hall;
see Example Hall
From: Holinshed's Chronicles of England, Scotland, and Ireland
Volume III, 1808
Richard the Third, third sonne to Richard duke of Yorke, and uncle to Edward the Fift.