Merriam-Webster's Collegiate® Dictionary, 11th Edition
WHISPER
I. verb (whispered; whispering) see: whistle Date: before 12th century intransitive verb to speak softly with little or no vibration of the vocal cords especially to avoid being overheard, to make a sibilant sound that resembles whispering, transitive verb to address in a whisper, to utter or communicate in or as if in a whisper,
II. noun
Date: 1595
something communicated by or as if by whispering,
2. an act or instance of whispering, a sibilant sound that resembles whispered speech, hint , trace