Fast fleet runs out: RN surrounds (7)
I believe the answer is:
ramadan
'fast fleet' is the definition.
'Ramadan' can be an answer for 'fast' (month of fasting in Islam). I'm unsure of the 'fleet' bit.
'runs out rn surrounds' is the wordplay.
'runs' becomes 'rams' ('ram' can be a synonym of 'run').
'out' means to remove the last letter.
'rn surrounds' becomes 'adan' (I can't explain this - if you can you should give a lot more credence to this answer).
'rams' with its last letter removed is 'ram'.
'ram'+'adan'='RAMADAN'
Can you help me to learn more?
(Other definitions for ramadan that I've seen before include "Moslem fast" , "The fasting month for Muslims, ninth of year" , "Ninth month of Muslim year, time to fast" , "Islamic month (of fasting)" , "Muslim period of fasting" .)