having the quality of flexibility without brittleness; yielding to force without breaking; capable of resisting great strain; as, the ligaments of animals are remarkably tough.-not easily broken; able to endure hardship; firm; strong; as, tough sinews.-not easily separated; viscous; clammy; tenacious; as, tough phlegm.-stiff; rigid; not flexible; stubborn; as, a tough bow.-severe; violent; as, a tough storm.