How to delete one specific file permanently in OS X Yosemite?
From what you said in your question, I'm assuming the file you want to delete is already in the Trash.


In Terminal (/Applications/Utilities/) type the rm command followed by a space.
Click the Trash Dock Tile to open a Finder window to the Trash. (Note that if the target file is not in the Trash just bring up the target file in Finder.)
Drag and drop the target file from the Trash (or whatever Finder window it's in) onto the Terminal window. This will add the fully qualified pathname of the file to be deleted to the rm command.
Example: rm /Users/me/.Trash/googlechrome.dmg
Press enter and the file should now deleted.


For additional options to the rm command have a look at: OS X Man Pages for rm

If the target is a folder use rm -dr ... where ... is the pathname of the folder to be deleted.