Sibilance is the sound someone makes when saying words that make the tongue push air through the front of the teeth, such as "zip" "jeep" "ship" and "chip". It can also refer to the non-word sounds that someone would make when getting someone's attention ("Ssst!") or telling one to be quiet ("shhhh!").
The sibilance in her voice is very pronounced.
by joe blows snow ho September 10, 2013