The Collaborative International Dictionary of English v.0.48:

Deferential \Def`er*en"tial\, a. [See Deference.]
   Expressing deference; accustomed to defer.
   [1913 Webster]

WordNet (r) 3.0 (2006):

deferential
    adj 1: showing deference [syn: deferent, deferential,
           regardful]