Croon

v. i.	1.	To make a continuous hollow moan, as cattle do when in pain.
	2.	To hum or sing in a low tone; to murmur softly. Here an old grandmother was crooning over a sick child, and rocking it to and fro. - Dickens.
	3.	To sing in a soft, evenly modulated manner adapted to amplifying systems, especially to sing in such a way with exaggerated sentimentality.
v. t.	1.	To sing in a low tone, as if to one's self; to hum. [imp. & p. p. Crooned (krŌnd); p. pr. & vb. n. Crooning.] Hearing such stanzas crooned in her praise. - C. Bronté.
	2.	To soothe by singing softly. The fragment of the childish hymn with which he sung and crooned himself asleep. - Dickens.
n.	1.	A low, continued moan; a murmur.
	2.	A low singing; a plain, artless melody.

Verb

1.

croon - sing softly

anthem, ballad, carol, chant, chirp, chirrup, choir, chorus, descant, do-re-mi, hum, hymn, intonate, intone, lilt, minstrel, pipe, psalm, quaver, roulade, serenade, shake, sing, sing in chorus, sol-fa, solmizate, tremolo, trill, troll, tweedle, tweedledee, twit, twitter, vocalize, warble, whistle, yodel