noun (n)

• a quiet or hushed tone of voice(noun.communication)

  Example:
  Spoke in undertones.
  

  source: wordnet30
• a subdued emotional quality underlying an utterance; implicit meaning(noun.cognition)

  Synonym:
  undercurrent
  

  source: wordnet30
• a pale or subdued color(noun.attribute)

  Synonym:
  tinge
  

  source: wordnet30
• A low or subdued tone or utterance; a tone less loud than usual.(noun)

  source: webster1913