Definition of "tuff"

This is what makes an ignimbrite; the general term for this kind of volcaniclastic rock is ‘tuff’.

2004, Richard Fortey, The Earth, Folio Society, published 2011, page 9n

Tuff Stuff teaches that while life may go smoothly most of the time, ...

1980, Joy Wilt Berry, Ernie Hergenroeder, Tuff Stuff: A Children's Book about Trauma‎, Educational Products Division, Word, Inc.

… yet never to make us so strong as the strongest of Men, whose Sinnews are tuffer, and Bones stronger, and Joints closer, and Flesh firmer, than ours are …

2000, Margaret Cavendish, “Preface to the Reader (1655)”, in Sylvia Bowerbank, Sara Mendelson, editors, Paper Bodies‎, page 139

It was rave reviewed in the Caribbean Times as 'the ruffest, tuffest and the boo-yacka of all modern gangster novels'.

2003, Ronald Carter, The Routledge Guide to Modern English Writing‎ (Language Arts), Routledge, page 96

TUFF METER

2006, Paige Hemmis, The Tuff Chix Guide to Easy Home Improvement‎, Penguin, page 36

Its Tuff-n-Tiny USB flash drive is about the size of a thumbnail. … The company insists that the "tuff" part of the name is well-earned for being waterproof, dustproof and you can drive a car over it.

2010 January 20, Robert J. Elisberg, “CES 2020 -- Ohm on the Range”, in Huffington Post‎, retrieved 2012-09-14

Tuff Stuff Professional Wrestling

2011, Kristian Pope, Tuff Stuff Professional Wrestling Field Guide: Legend and Lore‎, Krause Publications