The rate at which oceans turn round (5)
I believe the answer is:
speed
'the rate at which' is the definition.
'speed' can be an answer for 'the rate' (speed is a kind of rate). I'm unsure of the rest of the definition.
'oceans turn round' is the wordplay.
'oceans' becomes 'deeps' (I've seen this in another clue).
'turn round' says the letters should be written in reverse (I've seen 'turning round' mean this).
'deeps' in reverse letter order is 'SPEED'.
Can you help me to learn more?
(Other definitions for speed that I've seen before include "Travel quickly" , "Swiftness" , "Dispatch" , "Rate of movement" , "make rapid progress" .)