What is a synonym for challenging?

Here are some synonyms for "challenging," depending on the context:

General synonyms:

* Difficult

* Demanding

* Hard

* Tough

* Complex

* Rigorous

* Intricate

* Stressful

* Troublesome

* Testing

More specific synonyms:

* For tasks: demanding, arduous, taxing, strenuous, burdensome

* For people: provocative, confrontational, confrontative, stimulating

* For situations: precarious, uncertain, risky, precarious

For a more formal tone:

* Arduous

* Taxing

* Strenuous

* Burdensome

The best synonym will depend on the specific context of your sentence.