So he took the nice one out (5)
I believe the answer is:
hence
'so' is the definition.
(I know that so can be written as hence)
'he took the nice one out' is the wordplay.
'took' says to put letters next to each other.
'one' becomes 'i' (Roman numeral).
'out' indicates named letters should be taken away.
'nice' with 'i' taken out is 'nce'.
'he'+'nce'='HENCE'
(Other definitions for hence that I've seen before include "From this time, or for this reason" , "It follows from that fact" , "As a result" , "Therefore, consequently" , "Thus" .)