One-third power (4,4)
I believe the answer is:
cube root
'one-third power' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for cube root that I've seen before include "27's is 3" , "The 'x' in x3" , "As 7 is of 343" , "4 of 64 or 5 of 125, for example" , "3, of 27, for example?" .)