pretty tough = very/somewhat difficult, demanding, strict
The exam will be pretty tough.
They tell me the new professor is tough.
She is tough on/with her children.
Tough luck. = Bad luck.
In older slang (not current) "tough" meant exciting, good, nice, outstanding, etc. I have not heard "tough" used like that in years.
"Tough" can also mean strong and rugged (such as an opponent), difficult to chew (as in meat), etc.