Worn-out old reservists getting dry and cosy at last (5)
I believe the answer is:
tatty
'worn' is the definition.
(similar in meaning)
'old reservists getting dry and cosy at last' is the wordplay.
'old reservists' becomes 'TA' (Territorial Army, former name of UK Army Reserve).
'getting' is a charade indicator (letters next to each other).
'dry' becomes 'tt' (abbreviation for teetotal).
'and' is a charade indicator (letters next to each other).
'at last' indicates one should take the final letters.
The final letter of 'cosy' is 'y'.
'ta'+'tt'+'y'='TATTY'
'out' acts as a link.
(Other definitions for tatty that I've seen before include "of poor quality" , "Neglected" , "Showing signs of wear and tear" , "of inferior quality" , "untidy" .)