Merriam-Webster's Collegiate® Dictionary, 11th Edition
TOUGH
I. adjective
Etymology: Middle English, from Old English tōh; akin to Old High German zāhi tough Date: before 12th century
1. strong or firm in texture but flexible and not brittle, not easily chewed , glutinous , sticky , characterized by severity or uncompromising determination , capable of enduring strain, hardship, or severe labor , very hard to influence ; stubborn , difficult to accomplish, resolve, endure, or deal with , stubbornly fought , unruly , rowdyish , marked by absence of softness or sentimentality , see: strong toughly adverb toughness noun
II. adverb
Date: 14th century
in a tough manner ,
III. noun
Date: 1801
a tough person ; rowdy ,
IV. transitive verb
Date: 1830
to bear unflinchingly ; endure