Lute, if broken, is useless (6)
I believe the answer is:
futile
'useless' is the definition.
(similar in meaning)
'lute if broken' is the wordplay.
'broken' indicates an anagram.
'lute'+'if'='luteif'
'luteif' is an anagram of 'FUTILE'.
'is' is the link.
(Other definitions for futile that I've seen before include "Fruitless" , "Unavailing, a waste of time" , "Useless, a waste of effort" , "Ineffectual,in vain" , "Useless, pointless" .)