Wife has turned poet, holding old percussion instrument (9)
I believe the answer is:
washboard
'percussion instrument' is the definition.
(a washboard can be used as a musical instrument)
'wife has turned poet holding old' is the wordplay.
'wife' becomes 'w' (abbreviation).
'turned' indicates an anagram.
'poet' becomes 'bard' (bard is a kind of poet).
'holding' means one lot of letters goes inside another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'bard' enclosing 'o' is 'board'.
'has' is an anagram of 'ash'.
'w'+'ash'+'board'='WASHBOARD'
(Other definitions for washboard that I've seen before include "Skiffle instrument" , "On which to scrub clothes" , "It can be played" , "A percussion instrument" .)