Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Tenchthēri (Tenctēri), ōrum, m., a German people on the Rhine, in the neighborhood of the modern Cleves, Essen, and Bergen, Caes. B. G. 4, 1; 4, 4; 4, 16; Tac. G. 32; id. A. 13, 56; id. H. 4, 21.