I thought the translation of Gas was nwy! It turns out this is the mutated form for cas (as in cas gŵr ....) I don't think that mutated words should appear in isolation.
This is one of a number of entries which have already been deleted from the course database as a result of feedback during the current beta testing phase. Unfortunately there is a problem with the wider Duolingo system which is preventing them being removed from the system completely - and the course team cannot get at them to change them because they are not in the course database any more!
- cas - nasty
- gŵr cas - a nasty man
- cath gas - a nasty cat (mutation following a feminine noun)
- fy ngas beth - my pet hate/most hated thing - a particular meaning when this particular adjective is placed before the noun (mutation of beth caused by a preceding adjective)
- cas beth Owen - Owen's pet hate
- cath gas Owen - Owen's nasty cat
One workaround is to delete history from your browser, this often helps access to the most recent version of the course.
If you don't wish to lose your browser history then another alternative is to install another browser and use it only for Duolingo. One rarely used but nice one is Vivaldi.