Confuse hanger-on holding line (4)
I believe the answer is:
blur
'confuse' is the definition.
(synonyms)
'hanger-on holding line' is the wordplay.
'hanger-on' becomes 'bur' (type of seed which hangs onto clothing).
'holding' indicates putting letters inside.
'line' becomes 'l' (used when specifying particular lines from a poem).
'bur' placed around 'l' is 'BLUR'.
(Other definitions for blur that I've seen before include "British rock group" , "Indistinct appearance like smear" , "Muddle" , "Indistinct mark" , "Britpop band - indistinct vision" .)