Extremely short upturn can take your breath away (4)
I believe the answer is:
stun
'your breath away' is the definition.
I can't judge whether this definition defines the answer.
'extremely short upturn can take' is the wordplay.
'extremely' says to hollow out the word (remove centre letters) (only the extremes of the word are used).
'upturn' says the letters should be written in reverse (in a down clue, letters go up).
'can take' becomes 'nu' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'short' with its centre removed is 'st'.
'nu' backwards is 'un'.
'st'+'un'='STUN'
Can you help me to learn more?
(Other definitions for stun that I've seen before include "cause amazement" , "Dumbfound" , "Put out for the count" , "what a cracker may do?" , "Shock into silence" .)