The Collaborative International Dictionary of English v.0.48:

Knell \Knell\, v. t.
   To summon, as by a knell.
   [1913 Webster]

         Each matin bell, the baron saith,
         Knells us back to a world of death.      --Coleridge.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Knell \Knell\, n. [OE. knel, cnul, AS. cnyll, fr. cnyllan to
   sound a bell; cf. D. & G. knallen to clap, crack, G. & Sw.
   knall a clap, crack, loud sound, Dan. knalde to clap, crack.
   Cf. Knoll, n. & v.]
   The stroke of a bell tolled at a funeral or at the death of a
   person; a death signal; a passing bell; hence,
   (figuratively), a warning or harbinger of, or a sound
   indicating, the passing away of anything; -- also called
   death knell.
   [1913 Webster +PJC]

         The dead man's knell
         Is there scarce asked for who.           --Shak.
   [1913 Webster]

         The curfew tolls the knell of parting day. --Gray.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Knell \Knell\, v. i. [imp. & p. p. Knelled; p. pr. & vb. n.
   Knelling.] [OE. knellen, knillen, As. cnyllan. See Knell,
   n.]
   To sound as a knell; especially, to toll at a death or
   funeral; hence, to sound as a warning or evil omen.
   [1913 Webster]

         Not worth a blessing nor a bell to knell for thee.
                                                  --Beau. & Fl.
   [1913 Webster]

         Yet all that poets sing, and grief hath known,
         Of hopes laid waste, knells in that word, "alone".
                                                  --Ld. Lytton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

knell
    n 1: the sound of a bell rung slowly to announce a death or a
         funeral or the end of something
    v 1: ring as in announcing death
    2: make (bells) ring, often for the purposes of musical
       edification; "Ring the bells"; "My uncle rings every Sunday
       at the local church" [syn: ring, knell]

Moby Thesaurus II by Grady Ward, 1.0:

132 Moby Thesaurus words for "knell":
   annihilation, bane, bell, bemoan, bewail, biological death, bong,
   cessation of life, change ringing, chime, chiming, chink, clang,
   clanging, clangor, clank, clanking, clinical death, clink,
   coronach, crossing the bar, curtains, dead march, death,
   death bell, death knell, death song, debt of nature, decease,
   demise, departure, deplore, ding, ding-a-ling, dingdong, dinging,
   dingle, dirge, dissolution, dong, donging, doom, dying,
   ebb of life, elegize, elegy, end, end of life, ending, epicedium,
   eternal rest, eulogy, exit, expiration, extinction, extinguishment,
   final summons, finger of death, funeral march, funeral oration,
   funeral ring, funeral song, give sorrow words, going, going off,
   gong, grave, graveside oration, grieve, hand of death, jangle,
   jaws of death, jingle, jingle-jangle, jinglejangle, jingling, keen,
   knelling, lament, last debt, last muster, last rest, last roundup,
   last sleep, leaving life, loss of life, making an end, moan,
   monody, mourn, passing, passing away, passing bell, passing over,
   peal, peal ringing, pealing, perishing, quietus, release, repine,
   requiem, rest, reward, ring, ring changes, ringing,
   sentence of death, shades of death, shadow of death, sigh,
   sing the blues, sleep, somatic death, sorrow, sound, sound a knell,
   summons of death, threnode, threnody, ting, ting-a-ling, tingle,
   tingling, tink, tinkle, tinkling, tinnitus, tintinnabulate, toll,
   tolling, weep over