Definitions of silent:

• adjective:   marked by absence of sound

  Example: "A silent house"

• adjective:   having a frequency below or above the range of human audibility

  Example: "A silent dog whistle"

• adjective:   not made to sound

  Example: "The silent `h' at the beginning of `honor'"

• adjective:   failing to speak or communicate etc when expected to

  Example: "The witness remained silent"

• adjective:   indicated by necessary connotation though not expressed directly

  Example: "Gave silent consent"

• adjective:   unable to speak because of hereditary deafness