castrati

/K AH0 S T R AA1 T IY0/
noun
  1. 1

    A male who has been castrated, especially a male whose testicles have been removed before puberty in order to retain his boyish voice.

  2. 2

    A male soprano or alto voice produced by castration of the treble singer before puberty, intended to conserve his voice; the singer.

Source: https://en.wiktionary.org/wiki/castrati, https://en.wiktionary.org/wiki/castrato