The Collaborative International Dictionary of English v.0.48:

Croon \Croon\, v. t. [imp. & p. p. Crooned (kr[=oo]nd); p. pr.
   & vb. n. Crooning.]
   1. To sing in a low tone, as if to one's self; to hum.
      [1913 Webster]

            Hearing such stanzas crooned in her praise. --C.
                                                  Bront['e].
      [1913 Webster]

   2. To soothe by singing softly.
      [1913 Webster]

            The fragment of the childish hymn with which he sung
            and crooned himself asleep.           --Dickens.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

crooning \crooning\ n.
   1. singing in a soft low tone; as, her crooning soon put the
      child to sleep.
      [WordNet 1.5]

   2. the act of singing popular songs in a sentimental manner.
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

crooning
    n 1: singing in a soft low tone; "her crooning soon put the
         child to sleep"
    2: the act of singing popular songs in a sentimental manner