The Collaborative International Dictionary of English v.0.48:

Shrill \Shrill\, a. [Compar. Shriller; superl. Shrillest.]
   [OE. shril, schril; akin to LG. schrell, G. schrill. See
   Shrill,v. i.]
   Acute; sharp; piercing; having or emitting a sharp, piercing
   tone or sound; -- said of a sound, or of that which produces
   a sound.
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         Hear the shrill whistle which doth order give
         To sounds confused.                      --Shak.
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         Let winds be shrill, let waves roll high. --Byron.
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The Collaborative International Dictionary of English v.0.48:

Shrill \Shrill\, n.
   A shrill sound. [Obs.] --Spenser.
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The Collaborative International Dictionary of English v.0.48:

Shrill \Shrill\, v. i. [imp. & p. p. Shrilled; p. pr. & vb. n.
   Shrilling.] [OE. schrillen, akin to G. schrillen; cf. AS.
   scralletan to resound loudly, Icel. skr["o]lta to jolt, Sw.
   skr[aum]lla to shrill, Norw. skryla, skr?la. Cf. Skirl.]
   To utter an acute, piercing sound; to sound with a sharp,
   shrill tone; to become shrill.
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         Break we our pipes, that shrilledloud as lark.
                                                  --Spenser.
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         No sounds were heard but of the shrilling cock.
                                                  --Goldsmith.
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         His voice shrilled with passion.         --L. Wallace.
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The Collaborative International Dictionary of English v.0.48:

Shrill \Shrill\, v. t.
   To utter or express in a shrill tone; to cause to make a
   shrill sound.
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         How poor Andromache shrills her dolors forth. --Shak.
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WordNet (r) 3.0 (2006):

shrill
    adj 1: having or emitting a high-pitched and sharp tone or tones
           ; "a shrill whistle"; "a shrill gaiety" [syn: shrill,
           sharp]
    2: being sharply insistent on being heard; "strident demands";
       "shrill criticism" [syn: strident, shrill]
    3: of colors that are bright and gaudy; "a shrill turquoise"
    v 1: utter a shrill cry [syn: shriek, shrill, pipe up,
         pipe]

Moby Thesaurus II by Grady Ward, 1.0:

80 Moby Thesaurus words for "shrill":
   absonant, acute, argute, atonal, cacophonous, caterwaul, cracked,
   creak, creaky, diaphonic, disconsonant, discordant, disharmonic,
   disharmonious, dissonant, ear-piercing, ear-splitting, flat,
   grating, harsh, high, high-pitched, howl, howling, immelodious,
   inharmonic, inharmonious, keen, keening, musicless, nonmelodious,
   off, off-key, off-tone, out of pitch, out of tone, out of tune,
   penetrating, piercing, pipe, piping, raucous, reedy, screak,
   screaky, scream, screech, screeching, screechy, sharp, shriek,
   shrieking, shrieky, skirl, skreigh, sour, squawk, squeak,
   squeaking, squeaky, squeal, strident, thin, treble, tuneless,
   ululant, ululation, unharmonious, unmelodious, unmusical,
   untunable, untuned, untuneful, wail, wailing, whine, whining,
   whistle, whistling, yammer