Ev′a‐nesce″ (ĕv′ȧ‐nĕs″), v. i. [imp. & p. p.Evanesced (–nĕst″); p. pr. & vb. n.Evanescing. (–nĕs″sĭng).] [L. evanescere; e out + vanescere to vanish, fr. vanus empty, vain. See Vain, and cf. Evanish.] To vanish away; to become dissipated and disappear, like vapor.
I believe him to have evanesced or evaporated. De Quincey.