Constructed in the exact same way as the Swedish "dragningskraft" (meaning the same thing).
For the "grave seriousness" meaning you could use difrifwch "seriousness, earnestness, solemnity" or in some situations pwysigrwydd "importance".
Thank you shwmae, that's a big help. I can't seem to get on with that Geiriadur dictionary, so it's nice to be able to shout for help.
Geiriadur yr Academi is really for pretty advanced students. A better day-to-day one online is Geiriadur Bangor: http://geiriadur.bangor.ac.uk/ It can be downloaded as a free app too: https://www.bangor.ac.uk/canolfanbedwyr/ap_geiriaduron.php.en
@Hatakend I see what you mean about it being unfriendly in the search box. You can click "English" in the top right-hand corner for everything in English but even the search box should be bilingual on first arrival, then you make your choice of language. Fair point.
@Hatakend Dim problem. That site looks like it just goes through Google and Bing Translate, rather than being a source of reliable dictionary entries. That's fine, but just so that you're aware, those sites aren't always a reliable source of good modern translations. But I'd agree, with that proviso, use what works for you. Another site is http://www.gweiadur.com/en/Pawb. Pob hwyl / All the best!
@ibisc Yes, I've had that problem too. It's not always reliable on mobile. The site needs a bit of an overhaul. There are still parts of the dictionary that need further editing.
I have sometimes found that 'geiriaduracademi' is not accessible over a mobile phone network for some reason, but I have not found a problem with getting to it using wifi links.
The Bangor dictionary does seem less daunting, but giving instructions only in Welsh just feels unfriendly.