What does adust mean?
The definition of adust
A*dust”, a.
Etym: [L. adustus, p. p. of adurere: cf. F. aduste.]

1 Inflamed or scorched; fiery. “The Libyan air adust.” Milton.
2 Looking as if or scorched; sunburnt. A tall, thin man, of an adust complexion. Sir W. Scott.
3 (Med.)
Having much heat in the constitution and little serum in the blood. [Obs.] Hence: Atrabilious; sallow; gloomy.