1. 
   Senpai
   An honorific used by a young person when talking to or about a benefactor or senior in a social organization. The usage of this honorific is encountered time and again in anime, mostly when students are talking to or about their senior classmates. Used as a noun, it would just mean, "our seniors", o...
   Found op http://hubpages.com/hub/Anime-Dictionary
   
   
2. 
   Senpai
   Honorific used to address someone of higher status in an organization. May also be used to address someone of higher school status.
   Found op http://animeseed.com/index.php/anime-glossary
   
   
3. 
   senpai
   A title given to an upperclassman or other figure senior to the speaker.
   Found op http://www.usaanime.us/References/Glossary.htm
   
   

Tip: double click on a word to show its meaning.