Look good in charge, showing sound reasoning (5)
I believe the answer is:
logic
'sound reasoning' is the definition.
(I've seen this in another clue)
'look good in charge' is the wordplay.
'look' becomes 'lo' (archaic exclamation meaning 'look!').
'good' becomes 'g' (abbreviation).
'in charge' becomes 'ic' (abbreviation for 'in charge').
'lo'+'g'+'ic'='LOGIC'
'showing' is the link.
(Other definitions for logic that I've seen before include "4-ing" , "Rationale ?" , "using premises" , "Rational thinking" , "Reasoned thinking" .)