You can look for the Process ID in the top and similar programs, but kill and similar programs all search by process ID, not by name. Windows has the same problem, you must identify the program yourself, not simply type in a program name to finish the program.
Have you tried simply selecting the window and using the Alt-F4 key combination to close the window?
LMDE Mate 64-bit, LM17 Mate 64-bit
Debian Xfce 64-bit, Xubuntu 14.10 64-bit, Xubuntu 14.04 64-bit, Antergos Xfce 64-bit, PCLinuxOS LXDE 64-bit