Crossword Genius

Complacent, son, gullible person (4)

Ross

I believe the answer is:

smug

'complacent' is the definition.
(smug can mean complacent or self-satisfied)

'son gullible person' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'gullible person' becomes 'mug' (mug can mean a gullible or foolish person).
's'+'mug'='SMUG'

(Other definitions for smug that I've seen before include "Superior" , "Arrogantly complacent" , "Self-satisfied, complacent" , "Be envious of" , "Steal" .)

I've seen this clue in The Telegraph.
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