tough

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Able to withstand great strain without tearing or breaking; strong and resilient.
• adjective Hard to cut or chew.
• adjective Physically hardy; rugged.
• adjective Strong-minded; resolute.
• adjective Aggressive; pugnacious.
• adjective Inclined to violent or disruptive behavior; rowdy or rough.
• adjective Difficult to endure; severe; harsh.
• adjective Trying or unpleasant.
• adjective Difficult to deal with; demanding or troubling.
• adjective Informal Unfortunate; too bad.
• adjective Slang Fine; great.
• noun A violent or rowdy person; a hoodlum or thug.
• idiom (that's tough) Used to indicate recalcitrance or noncompliance with a complaint or demand.
• idiom (tough it out) To get through despite hardship; endure.

from The Century Dictionary.

• Having the property of flexibility without brittleness; yielding to a bending force without breaking; also, hard to cut or sever, as with a cutting-instrument: as, tough meat.
• Firm; strong; able to endure hardship, hard work, or ill usage; hardy; not easily broken or impaired.
• Not easily separated; tenacious; stiff; ropy; viscous: as, a tough clay; tough phlegm.
• Not easily influenced; unyielding; stubborn; hardened; incorrigible.
• Hard to manage or accomplish; difficult; trying; requiring great or continued effort.
• Severe; violent: as, a tough rebuke or tirade; a tough storm.
• noun A rough; a bully; an incorrigibly vicious fellow; a bad character.

from the GNU version of the Collaborative International Dictionary of English.

• noun A person who is tough{7}; a ruffian; a thug.
• adjective Having the quality of flexibility without brittleness; yielding to force without breaking; capable of resisting great strain.
• adjective Not easily broken; able to endure hardship; firm; strong; -- of objects and people.
• adjective Not easily separated; viscous; clammy; tenacious.
• adjective Stiff; rigid; not flexible; stubborn.
• adjective colloq. Severe; violent.
• adjective Difficult to do, perform, or accomplish.
• adjective Prone to aggressive or violent behavior; rowdyish; -- of people, or groups.
• adjective [Obs.] to make it a matter of difficulty; to make it a hard matter.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Strong and resilient; sturdy.
• adjective of food Difficult to cut or chew.
• adjective Rugged or physically hardy.
• adjective Stubborn.
• adjective of weather, etc. Harsh or severe.
• adjective Rowdy or rough.
• adjective etc. Difficult or demanding.
• adjective material science Undergoing plastic deformation before breaking.
• interjection slang Used to indicate lack of sympathy
• noun A person who obtains things by force; a thug or bully.
• verb To endure.
• verb To toughen.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective making great mental demands; hard to comprehend or solve or believe
• noun an aggressive and violent young criminal
• noun someone who learned to fight in the streets rather than being formally trained in the sport of boxing
• adjective unfortunate or hard to bear
• adjective substantially made or constructed