Undertake seriously to use bad language (5)

I believe the answer is:

swear

I'm a little stuck... Click here to teach me more about this clue!

This clue could be a double definition.

'undertake seriously' is the first definition.
'swear' can be an answer for 'undertake' (thesaurus). I am not certain of the 'seriously' bit.

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

'to' acts as a link.

Can you help me to learn more?

(Other definitions for swear that I've seen before include "Affirm" , "Promise on oath" , "Emit oath or take vow" , "Vow, attest" , "Express annoyance" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.