The story
Originally named "gray sulphuret of copper in dodecahedral crystals" in 1817 by mineralogist James Sowerby. Renamed in 1819 by William Phillips in honour of Smithson Tennant (1761-1815), an English chemist who discovered the elements iridium and osmium. Tennant + -ite
Etymology from Wiktionary, CC BY-SA 4.0.