Deteriorate for some days at the end of the month (5)
I believe the answer is:
decay
'deteriorate' is the definition.
(thesaurus)
'some days at the end of the month' is the wordplay.
'some' becomes 'a'.
'days' becomes 'y' (I can't explain this - if you can you should believe this answer much more).
'at the end of' is a charade indicator (letters next to each other).
'the month' becomes 'Dec' (abbreviation for December).
'a'+'y'='ay'
'ay' put after 'dec' is 'DECAY'.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for decay that I've seen before include "Atrophy" , "Deterioration" , "Decompose or fall into ruin" , "Briefly fashionable" , "Rot, perish" .)