Ruler way back, initially named in song (7)
I believe the answer is:
tsarina
'ruler' is the definition.
(I've seen this before)
'way back initially named in song' is the wordplay.
'way' becomes 'st' ().
'back' is a reversal indicator.
'initially' says to take the initial letters.
'in' indicates putting letters inside.
'song' becomes 'aria' (aria is a kind of song).
The initial letter of 'named' is 'n'.
'st' in reverse letter order is 'ts'.
'n' put into 'aria' is 'arina'.
'ts'+'arina'='TSARINA'
(Other definitions for tsarina that I've seen before include "Russian noblewoman" , "Monarch" , "Nicholas's wife" , "aristocratic woman" , "Russian royal; Sinatra (anag.)" .)