Silly me, I assumed that the executable path was the requirement. My bad. If you need to find a process just by it's name, it is even simpler: Just indicate the process name (possibly with wildcards) to Get-Process (alias ps):

ps Notepad++ | kill

Actually, kill (alias for Stop-Process) takes a name parameter directly, so the "kill" line from the script could be written as simply

kill notepad++

But your question is actually really good, because what if we did not know the neither the process name nor the executable, but -say- only the Window title? Get-process (alias ps) will produce a sequence objects describing the running processes. If I want to know what properties those objects have that I can possibly filter on, I can pipe the objects through the Get-Member cmdlet (alias gm):

    ps | gm

This produces a table-formatted list like this (shortened):

    TypeName: System.Diagnostics.Process

    Name                       MemberType     Definition
    ----                       ----------     ----------
    Handles                    AliasProperty  Handles = Handlecount
    Name                       AliasProperty  Name = ProcessName
	...
    MainModule                 Property       System.Diagnostics.ProcessModule MainModule {get;}
    MainWindowHandle           Property       System.IntPtr MainWindowHandle {get;}
    MainWindowTitle            Property       string MainWindowTitle {get;}
    MaxWorkingSet              Property       System.IntPtr MaxWorkingSet {get;set;}
	...
    Site                       Property       System.ComponentModel.ISite Site {get;set;}
    StandardError              Property       System.IO.StreamReader StandardError {get;}
    StandardInput              Property       System.IO.StreamWriter StandardInput {get;}
    StandardOutput             Property       System.IO.StreamReader StandardOutput {get;}
    StartInfo                  Property       System.Diagnostics.ProcessStartInfo StartInfo {get;set;}
	...
    Product                    ScriptProperty System.Object Product {get=$this.Mainmodule.FileVersionInfo.ProductName;}
    ProductVersion             ScriptProperty System.Object ProductVersion {get=$this.Mainmodule.FileVersionInfo.ProductVersion;}

Lo and behold, there is a property called MainWindowTitle. So to stop a process by it's main window title I could write:

    ps | ? MainWindowTitle -eq 'Deepthought Main Console' | kill

That is, find all processes, pipe them through a filter selecting only those where the MainWindowTitle equals the desired text, and pipe those processes to the Stop-Process cmdlet