N refers to new window:

Command-N：New Window
Shift-Command-N：Reopen the last window you closed

T refers to new tab:

Command-T: New Tab
Shift-Command-T：Reopen the last tab you closed

W refers to Withdraw:

Command-W: Close the active tab.
Shift-Command-W: Close Window

I thought W referred to Window…and often closed tabs and windows unintentionally…