tough -- (not given to gentleness or sentimentality; "a tough character")
rugged, tough -- (very difficult; severely testing stamina or resolution; "a rugged competitive examination"; "the rugged conditions of frontier life"; "the competition was tough"; "it's a tough life"; "it was a tough job")
tough, toughened -- (physically toughened; "the tough bottoms of his feet")
sturdy, tough -- (substantially made or constructed; "sturdy steel shelves"; "sturdy canvas"; "a tough all-weather fabric"; "some plastics are as tough as metal")
ruffianly, tough -- (violent and lawless; "the more ruffianly element"; "tough street gangs")
bad, tough -- (feeling physical discomfort or pain (`tough' is occasionally used colloquially for `bad'); "my throat feels bad"; "she felt bad all over"; "he was feeling tough after a restless night")
tough -- (resistant to cutting or chewing)
hard, tough -- (unfortunate or hard to bear; "had hard luck"; "a tough break")
baffling, elusive, knotty, problematic, problematical, tough -- (making great mental demands; hard to comprehend or solve or believe; "a baffling problem"; "I faced the knotty problem of what to have for breakfast"; "a problematic situation at home")