The Collaborative International Dictionary of English v.0.48:

Overtone \O"ver*tone`\, n. [A translation of G. oberton. See
   Over, Tone.] (Mus.)
   One of the harmonics faintly heard with and at a higher
   frequency than a fundamental tone as it dies away, produced
   by some aliquot portion of the vibrating sting or column of
   air which yields the fundamental tone; one of the natural
   harmonic scale of tones, as the octave, twelfth, fifteenth,
   etc.; an aliquot or "partial" tone; a harmonic. See
   Harmonic, and Tone. --Tyndall.
   [1913 Webster]

WordNet (r) 3.0 (2006):

overtone
    n 1: (usually plural) an ulterior implicit meaning or quality;
         "overtones of despair"
    2: a harmonic with a frequency that is a multiple of the
       fundamental frequency [syn: overtone, partial, partial
       tone]

Moby Thesaurus II by Grady Ward, 1.0:

105 Moby Thesaurus words for "overtone":
   AF, affective meaning, air, allegory, allusion, arcane meaning,
   assumption, atmosphere, audio frequency, aura, bearing, climate,
   coloration, coloring, connotation, consequence, denotation, drift,
   effect, essence, extension, feel, feeling, flageolet tone, force,
   frequency, fundamental, fundamental tone, gist,
   grammatical meaning, harmonic, harmonic tone, hint, idea, impact,
   implication, implied meaning, import, indication, inference,
   innuendo, insinuation, intension, intimation, intonation,
   ironic suggestion, lexical meaning, literal meaning, meaning,
   metaphorical sense, milieu, monotone, monotony, note, nuance,
   occult meaning, partial, partial tone, pertinence, pitch, pith,
   point, practical consequence, presumption, presupposition, purport,
   quality, range of meaning, real meaning, reference, referent,
   relation, relevance, scope, semantic cluster, semantic field,
   sense, significance, signification, significatum, signifie,
   span of meaning, spirit, structural meaning, subsense,
   subsidiary sense, substance, suggestion, sum, sum and substance,
   supposition, symbolic meaning, symbolism, tenor, tinge, tone,
   tonelessness, totality of associations, touch, transferred meaning,
   unadorned meaning, undercurrent, undermeaning, undertone, value