The Collaborative International Dictionary of English v.0.48:

Advertent \Ad*vert"ent\, a. [L. advertens, -entis, p. pr. of
   advertere. See Advert.]
   Attentive; heedful; regardful. --Sir M. Hale. --
   Ad*vert"ent*ly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

advertent
    adj 1: giving attention [syn: advertent, heedful]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "advertent":
   agog, alert, all ears, all eyes, assiduous, attentive, aware,
   careful, concentrated, conscious, diligent, earnest, finical,
   finicking, finicky, heedful, intense, intent, intentive,
   meticulous, mindful, nice, niggling, observant, observing,
   on the ball, on the job, open-eared, open-eyed, openmouthed,
   regardful, watchful