London Underground entrance about to close early (4)
I believe the answer is:
tube
'london underground' is the definition.
(I've seen this in another clue)
'entrance about to close early' is the wordplay.
'entrance' becomes 'ube' (I can't explain this - if you can you should give a lot more credence to this answer).
'about' means one lot of letters go next to another.
'close early' means to remove the last letter (I've seen 'closing early' mean this).
'to' with its final letter taken off is 't'.
'ube' put after 't' is 'TUBE'.
Can you help me to learn more?
(Other definitions for tube that I've seen before include "Underground transport" , "Can of beer (colloquial)" , "Valve" , "Transport system" , "Pipe; underground train" .)