The Collaborative International Dictionary of English v.0.48:

Grateful \Grate"ful\, a. [Grate, a. + full; cf. F. gr['e]
   thanks, good will, fr. L. gratum, neut. of gratus agreeable,
   grateful. See Grate, a.]
   1. Having a due sense of benefits received; kindly disposed
      toward one from whom a favor has been received; willing to
      acknowledge and repay, or give thanks for, benefits; as, a
      grateful heart.
      [1913 Webster]

            A grateful mind
            By owing, owes not, but still pays.   --Milton.
      [1913 Webster]

   2. Affording pleasure; pleasing to the senses; gratifying;
      delicious; as, a grateful present; food grateful to the
      palate; grateful sleep.
      [1913 Webster]

            Now golden fruits on loaded branches shine,
            And grateful clusters swell.          --Pope.

   Syn: Thankful; pleasing; acceptable; gratifying; agreeable;
        welcome; delightful; delicious. -- Grate"ful*ly, adv.
        -- Grate"ful*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

grateful
    adj 1: feeling or showing gratitude; "a grateful heart";
           "grateful for the tree's shade"; "a thankful smile" [syn:
           grateful, thankful] [ant: thankless, ungrateful,
           unthankful]
    2: affording comfort or pleasure; "the grateful warmth of the
       fire"