Many words in English end in either -ious or -eous and it can be hard to know which ending to choose.
Most words that have a 'sh' sound just before the ending are spelt -ious.
For example:
cautious
vicious
conscious
However, there are no other rules to help and unfortunately it is just a case of learning which ending to use!
As always, with tricky spellings, the more you read and the more you practise, the easier it will become!
Let's start right now!