theine (??i?i?n; -?n) n (Elements & Compounds) another name for caffeine, esp when present in tea[C19: from New Latin thea tea + -ine2]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014