double-dealing vs deceit

double-dealing and deceit both are nouns.

Word	Noun	Adjective	Verb	Adverb
double-dealing	Yes	Yes	No	No
deceit	Yes	No	No	No

As nouns, deceit is a hypernym of double-dealing; that is, deceit is a word with a broader meaning than double-dealing:

double-dealing: acting in bad faith; deception by pretending to entertain one set of intentions while acting under the influence of another
deceit: the act of deceiving

Other hypernyms of double-dealing include deception, dissembling, dissimulation.

double-dealing (noun)	deceit (noun)
acting in bad faith; deception by pretending to entertain one set of intentions while acting under the influence of another	the act of deceiving
	the quality of being fraudulent
	a misleading falsehood

double-dealing (adjective)	deceit (adjective)
marked by deliberate deceptiveness especially by pretending one set of feelings and acting under the influence of another