Webster’s Revised Unabridged Dictionary · 1913
Soothfast
Sooth′fast′ (so͞oth′fȧst′), a. [Sooth + fast, that is, fast or firm with respect to truth.] Firmly fixed in, or founded upon, the thruth; true; genuine; real; also, truthful; faithful. [Archaic] — Sooth′fast′ness, n. [Archaic] "In very soothfastness." Chaucer.
Why do not you . . . bear leal and soothfast evidence in her behalf, as ye may with a clear conscience! Sir W. Scott.
Sooth′fast′, adv. Soothly; really; in fact. [Archaic]
I care not if the pomps you show Be what they soothfast appear. Emerson.