Promise kept by goatherd (4)

I believe the answer is:

oath

'promise' is the definition.
(thesaurus)

'kept by goatherd' is the wordplay.
'kept by' indicates the answer is hidden within the clue.
'OATH' is hidden within 'goatherd'.

(Other definitions for oath that I've seen before include "Swear word" , "'Profane, or solemn expression (4)'" , "Curse or solemn word" , "Swearword or solemn word" , "bad language" .)

I've seen this clue in The Telegraph.

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