sen·sei (s?n?s??, s?n-s??)n. pl. sen·seis 1. A teacher or mentor, especially of a martial art.2. Used as a form of address for such a person.[Japanese, teacher, master, from Middle Chinese sian?a?j?, elder, prior-born (term of respect) (also the source of Mandarin xi?nsheng) : sian, first + ?a?j?, to give birth, be born (ultimately from Proto-Sino-Tibetan *sri?, live, life; also the source of Burmese hrang, live, alive).]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.sensei (?s?nse?) n, pl sensei (Judo & Karate) a Japanese title for a teacher, master, or professional; (in English) used esp for a martial arts teacher[Japanese: teacher, leader]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014