1868, John Christopher Atkinson, A glossary of the Cleveland dialect: explanatory, derivative, and critical, A. and C. Black:
Teugh, adj. (Pr. of the eu much as in Teuflt). Tough.
"With cordes enewe and ropys Teugh
The Jues felle my limmes out-droghe
For that I was not mete enoghe
Unto the bore"
1897, William Dwight Whitney, Benjamin Eli Smith, The Century dictionary and cyclopedia: a work of universal reference in all departments of knowledge, with a new atlas of the world, Volume 8, Century:
A dialectical (Scottish) form of tough.
"Unco thick in the soles, as ye may weel mind, forbye being teugh in the upper-leather."