Unwavering rose design on instrument (8)
I believe the answer is:
resolute
'unwavering' is the definition.
(similar in meaning)
'rose design on instrument' is the wordplay.
'design' indicates anagramming the letters.
'on' is a charade indicator (letters next to each other).
'instrument' becomes 'lute' (lute is a kind of instrument).
'rose' is an anagram of 'reso'.
'reso'+'lute'='RESOLUTE'
(Other definitions for resolute that I've seen before include "'With fixed purpose, steadfast (8)'" , "Determined, firm" , "Admirably purposeful" , "in a determined manner" , "without flinching" .)