What is another word for tough?

The best synonym for "tough" depends on the context. Here are some options, depending on the meaning you want to convey:

For physical toughness:

* Strong

* Sturdy

* Durable

* Robust

* Resilient

* Hard

* Solid

* Unbreakable

For mental toughness:

* Resilient

* Determined

* Persistent

* Tenacious

* Strong-willed

* Unyielding

* Indomitable

* Gritty

For difficulty:

* Difficult

* Challenging

* Hard

* Demanding

* Intense

* Rigorous

* Strained

For being harsh or unkind:

* Cruel

* Ruthless

* Merciless

* Unforgiving

* Unfeeling

* Hard-hearted

For being unpleasant:

* Unpleasant

* Rough

* Uncomfortable

* Difficult

* Awkward

* Unfavorable

Please provide more context about how you're using the word "tough" and I can give you a more specific synonym.