Instrument of victory I look up (4)
I believe the answer is:
viol
'instrument' is the definition.
(viol is a kind of instrument)
'victory i look up' is the wordplay.
'victory' becomes 'v'.
'look' becomes 'lo'.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'lo' reversed gives 'ol'.
'v'+'i'+'ol'='VIOL'
'of' acts as a link.
(Other definitions for viol that I've seen before include "Old string instrument" , "Old six-stringed instrument played with a bow" , "Double bass relative" , "something from the past to play" , "Early fiddle" .)