Reversal of number, current, current, number (7)
I believe the answer is:
edition
'number' is the definition.
(edition is a kind of number)
'reversal of number current current' is the wordplay.
'reversal of' says the letters should be written in reverse.
'number' becomes 'no' (abbreviation for 'number').
'current' becomes 'i' (symbol for electric current).
'current' becomes 'tide' (I've seen this before).
'no'+'i'+'tide'='noitide'
'noitide' written backwards gives 'EDITION'.
(Other definitions for edition that I've seen before include "Newspaper issue" , "Volume" , "(Copy from) single print run" , "Copies of book printed from one set of type" , "Particular form of a published text" .)