ivory  
noun uk/ˈaɪ.vər.i/ us/ˈaɪ.vɚ.i/
  (SUBSTANCE)         
 [ U ]象牙 
the hard yellowish-white substance that forms the tusks of some animals such as elephants, used especially in the past to make decorative objects
  Ivory is a softer material than you might imagine.
 a ban on ivory trading 象牙交易禁令 
  [ C usually plural ]象牙制品 
an object made from ivory
  a collection of Japanese ivories 日本象牙制品藏品 
 Idiom   
tickle the ivoriesidiom  old-fashioned humorous 弹钢琴
to play the piano
  He's the piano teacher who taught my daughter to tickle the ivories.