The Collaborative International Dictionary of English v.0.48:

Respectful \Re*spect"ful\ (-f?l), a.
   Marked or characterized by respect; as, respectful
   deportment.
   [1913 Webster]

         With humble joy and with respectful fear. --Prior.
   [1913 Webster] -- Re*spect"ful*ly, adv. --
   Re*spect"ful*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

respectful
    adj 1: full of or exhibiting respect; "respectful behavior"; "a
           respectful glance" [ant: disrespectful]
    2: feeling or manifesting veneration [syn: respectful,
       reverential, venerating]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "respectful":
   acclamatory, accommodating, admiring, affable, agreeable,
   appreciative, approbatory, attentive, cap in hand, ceremonious,
   civil, commendatory, complaisant, complimentary, conscientious,
   considerate, cordial, courteous, deferential, duteous, dutiful,
   encomiastic, ethical, eulogistic, fair, flattering, gentlemanly,
   graceful, gracious, honorific, ladylike, laudatory, mannerly,
   moral, obedient, obliging, observant, panegyric, polite, regardful,
   reverent, reverential, scrupulous, solicitous, tactful, thoughtful,
   urbane, well-behaved, well-mannered