Bad language used in boathouse (4)

I believe the answer is:

oath

'bad language' is the definition.
(I've seen this before)

'in boathouse' is the wordplay.
'in' says the answer is hidden in the clue.
'OATH' is hidden within 'boathouse'.

'used' is the link.

(Other definitions for oath that I've seen before include "A curse or solemn declaration" , "Profane or obscene expression" , "Courtroom promise" , "Swear word" , "Sworn declaration" .)

I've seen this clue in The Sun.

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