The Collaborative International Dictionary of English v.0.48:

Regardful \Re*gard"ful\ (-f?l), a.
   Heedful; attentive; observant. -- Re*gard"ful*ly, adv.
   [1913 Webster]

         Let a man be very tender and regardful of every pious
         motion made by the Spirit of God to his heart. --South.
   [1913 Webster]

   Syn: Mindful; heedful; attentive; observant.
        [1913 Webster]

WordNet (r) 3.0 (2006):

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