Bother from unexpected source — swear initially! (4)

I believe the answer is:

fuss

'bother' is the definition.
(synonyms)

'from unexpected source swear initially' is the wordplay.
'initially' suggests taking the first letters.
The first letters of 'from unexpected source swear' is 'FUSS'.

(Other definitions for fuss that I've seen before include "Unnecessary excitment or bother" , "Furore" , "Protest -- excitement" , "trouble" , "Needless excitement" .)

I've seen this clue in The Times.

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