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 definition and answer can be both states of affairs as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'a month and a year without attention' is the wordplay.
'a month' becomes 'Dec' (abbreviation for December).
'and' says to put letters next to each other.
'without' indicates named letters should be taken away.
'attention' becomes 'ear' (having someone's ear is having their attention).
'year' with 'ear' taken out 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)'" .)