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apparently a shortened form of dedeignous, disdainous, French dédaigneux, Old French desdeignous (12th c. in Hatzf.)
(Earlier examples of dedeignous, dedainous, than of deignous are not yet known; but the history of disdain shows that they may well have existed.)
From: A Select Collection of Old Plays
The Second Edition. Volume the Tenth, 1780
The Ordinary. William Cartwright.
Act III. Scene I