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]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "deferential":
   accommodating, affable, agreeable, attentive, cap in hand,
   ceremonious, civil, complaisant, conscientious, considerate,
   courteous, crouching, disarming, duteous, dutiful, ethical, fair,
   graceful, gracious, honorific, insinuating, insinuative, moral,
   obedient, obeisant, obliging, obsequious, observant,
   on bended knee, polite, prone, prostrate, regardful, respectful,
   saccharine, scrupulous, servile, silken, silky, solicitous,
   subservient, tactful, thoughtful, urbane