The Collaborative International Dictionary of English v.0.48:

Perdurable \Per*dur"a*ble\ (p[~e]r*d[=u]r"[.a]*b'l; 277), n.
   [Cf. F. perdurable, OE. pardurable. See Perdure.]
   Very durable; lasting; continuing long. [Archaic] --Chaucer.
   --Shak.
   [1913 Webster] -- Per*dur"a*bly, adv. [Archaic]
   [1913 Webster] Perdurance