Cancel split window in Vim

Press Control+w, then hit q to close each window at a time.

Update: Also consider eckes answer which may be more useful to you, involving :on (read below) if you don't want to do it one window at a time.

To close all splits, I usually place the cursor in the window that shall be the on-ly visible one and then do :on which makes the current window the on-ly visible window. Nice mnemonic to remember.

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Edit: :help :on showed me that these commands are the same:

• :on
• :only
• CTRL-w CTRL-o
• And yes, also CTRL-W o has the same effect (as Nathan answered).

Each of these four closes all windows except the active one.