1. superlative form of tough: most difficult to do or deal with
2. superlative form of tough: strongest or most durable
3. superlative form of tough: most strict or severe

Examples

• This is the toughest math problem I’ve ever seen.
• She’s the toughest competitor in the league.
• The final exam was the toughest part of the course.
• Steel is one of the toughest materials available.
• He’s known as the toughest judge in the courthouse.
• The toughest part of the hike is the steep climb at the end.
• This fabric is the toughest we manufacture.