A month and a year without attention is a bad thing (5)
I believe the answer is:
decay
'a bad thing' is the definition.
The answer and definition can be both states of affairs as well as being singular nouns.
Maybe you can see a link between them that I don't see?
'a month and a year without attention' is the wordplay.
'a month' becomes 'dec' (abbreviation for December).
'and' means one lot of letters go next to another.
'without' is a deletion indicator.
'attention' becomes 'ear' (having someone's ear is having their attention).
'year' with 'ear' removed is 'y'.
'dec'+'a'+'y'='DECAY'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for decay that I've seen before include "Atrophy" , "Putrefy" , "Deterioration" , "Decompose or fall into ruin" , "'Decompose, rot (5)'" .)