Tattoo received by old man less well — this might be required (10)

I believe the answer is:
painkiller
'this might be required' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'tattoo received by old man less well' is the wordplay.
'tattoo' becomes 'ink' (ink can informally mean a tattoo).
'received by' is an insertion indicator.
'old man' becomes 'pa' (both can mean someone's father).
'less well' becomes 'iller' ('ill' can be the opposite of 'well' so perhaps 'iller' is reasonable for 'less well').
'pa'+'iller'='pailler'
'ink' inserted inside 'pailler' is 'PAINKILLER'.
Can you help me to learn more?
(Other definitions for painkiller that I've seen before include "Analgesic drug" , "Aspirin, for instance" , "form of medicine" , "soothing drug" , "Aspirin maybe" .)
