"a tough character"

"a rugged competitive examination"
"the rugged conditions of frontier life"
"the competition was tough"
"it's a tough life"
"it was a tough job"

"the tough bottoms of his feet"

"sturdy steel shelves"
"sturdy canvas"
"a tough all-weather fabric"
"some plastics are as tough as metal"

"the more ruffianly element"
"tough street gangs"

"my throat feels bad"
"she felt bad all over"
"he was feeling tough after a restless night"

"had hard luck"
"a tough break"

"a baffling problem"
"I faced the knotty problem of what to have for breakfast"
"a problematic situation at home"