Self-satisfied son, fool (4)

I believe the answer is:

smug

'self-satisfied' is the definition.
(synonyms)

'son fool' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'fool' becomes 'mug' (synonyms).
's'+'mug'='SMUG'

(Other definitions for smug that I've seen before include "goody-goody" , "Self-righteous" , "irritating expression" , "Like a stuffed shirt" , "Irritatingly self-satisfied" .)

I've seen this clue in The Times.

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