Line in bootees unfortunately no longer in use (8)
I believe the answer is:
obsolete
'no longer in use' is the definition.
(I've seen this before)
'line in bootees unfortunately' is the wordplay.
'line' becomes 'l'.
'in' is an insertion indicator.
'unfortunately' is an anagram indicator.
'bootees' anagrammed gives 'obsoete'.
'l' inserted into 'obsoete' is 'OBSOLETE'.
(Other definitions for obsolete that I've seen before include "Discontinued" , "No longer current" , "Old hat" , "being out of practice" , "Out-of-date" .)