Damage one flute that is useless (6)
I believe the answer is:
futile
'useless' is the definition.
(similar in meaning)
'damage one flute' is the wordplay.
'damage' indicates anagramming the letters (I've seen this in other clues).
'one' becomes 'I' (Roman numeral).
'i'+'flute'='iflute'
'iflute' is an anagram of 'FUTILE'.
'that is' is the link.
(Other definitions for futile that I've seen before include "Ineffective" , "Ineffectual, vain" , "Trifling and ineffectual" , "In vain, a waste of time" , "Ineffectual, unavailing" .)