From Longman Dictionary of Contemporary Englishtoughentough‧en /ˈtʌfən/ (also toughen up) verb [intransitive, transitive] HARDSTRONG PERSONto become tougher, or to make someone or something tougher toughened glass Three years in the army toughened him up.→ See Verb table
Examples from the Corpus
toughen• The schools claimed to toughen boys, and they did.• The state is toughening its anti-smoking laws.• Governor Bush has made his mark building prisons, toughening laws on juvenile crime and calling for lower property taxes.• Even better would be cake flour, which contains even less of those toughening proteins, she said.• Just the opposite is true with cake, muffin or quick-bread recipes where too much gluten will toughen the finished product.• Both conservatives and Communists have simply toughened their attitude to the government.• Thus, cotton consists of cellulose; and so does wood, though wood is toughened with lignin. 