(1):

(n.) To sound as a knell; especially, to toll at a death or funeral; hence, to sound as a warning or evil omen.

(2):

(n.) The stoke of a bell tolled at a funeral or at the death of a person; a death signal; a passing bell; hence, figuratively, a warning of, or a sound indicating, the passing away of anything.

(3):

(v. t.) To summon, as by a knell.