Chart-topper with other arrangement previously (8)
I believe the answer is:
hitherto
'previously' is the definition.
(I've seen this before)
'chart-topper with other arrangement' is the wordplay.
'chart-topper' becomes 'hit' (I've seen this in another clue).
'with' means one lot of letters go next to another.
'arrangement' indicates anagramming the letters.
'other' is an anagram of 'herto'.
'hit'+'herto'='HITHERTO'
(Other definitions for hitherto that I've seen before include "Up to this point" , "Up to this time" , "So far" , "Up till now" , "Previously" .)