v. i. - To make a continuous hollow moan, as cattle do when in pain.
v. i. - To hum or sing in a low tone; to murmur softly.
v. t. - To sing in a low tone, as if to one's self; to hum.
v. t. - To soothe by singing softly.
n. - A low, continued moan; a murmur.
n. - A low singing; a plain, artless melody.