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]

Moby Thesaurus II by Grady Ward, 1.0:

108 Moby Thesaurus words for "regardful":
   acclamatory, accommodating, accommodative, active, admiring,
   advertent, agog, agreeable, alert, all ears, all eyes,
   appreciative, approbatory, assiduous, attentive, aware, canny,
   cap in hand, careful, cautious, ceremonious, circumspect,
   commendatory, complaisant, compliant, complimentary, concentrated,
   conforming, conscientious, conscious, considerate, constant,
   courteous, curious, deferential, deliberate, delicate, devoted,
   devout, diligent, discreet, duteous, dutiful, earnest, encomiastic,
   eulogistic, faithful, finical, finicking, finicky, flattering,
   gingerly, guarded, heedful, helpful, hesitant, honorific,
   indulgent, intense, intent, intentive, judicious, laudatory,
   leaving out nothing, lenient, loving, loyal, meticulous, mindful,
   mindful of others, nice, niggling, noncommittal, obliging,
   observant, observing, on guard, on the ball, on the job,
   open-eared, open-eyed, openmouthed, overlooking no possibility,
   panegyric, pawky, politic, practicing, prudent, punctilious,
   punctual, respectful, safe, scrupulous, slow to act, solicitous,
   tactful, tender, tentative, thorough, thoughtful, tolerant, true,
   unadventurous, uncommunicative, undaring, unenterprising,
   unprecipitate, watchful