Old hat blooming tatty (7)
I believe the answer is:
outworn
'old' is the definition.
(thesaurus)
'blooming tatty' is the wordplay.
'blooming' becomes 'out' (plants which have bloomed are 'out').
'tatty' becomes 'worn' (similar in meaning).
'out'+'worn'='OUTWORN'
'hat' is the link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for outworn that I've seen before include "Old, exhausted or no longer used as dress" , "Obsolete, dated" , "Jaded" , "Old-fashioned" , "Out of date" .)