What does "intention" mean? I see two Pali words which are translated into English as "intention":


Cetanā used in the definition of karma
Sankappa used in the definition of the Noble Eightfold Way.


Do these two words mean exactly the same thing? If not, what is the difference?
Cetana is executed by action, speech and thinking. 


Samma Sankappa - Right Thinking 
Samma Vaca - Right Speech 
Samma Kammantha - Right Action 


So the difference is Cetana includes speech and action where as Sankappa by itself only includes thinking. 

Please note that "Right" here is explained properly by Samma Ditti and doesn't mean right action in general sense (eg. Teaching, Nursing).