Are you looking for a comprehensive ECG glossary that goes beyond simply defining words? Dr. Ken Grauer, who is the ECG Guru's Consulting Expert, has a Glossary available on his website that explains the terms.  Instructors and students alike will benefit from having this glossary readily available.  The glossary is exerpted from his e-Publication, "A 1st Book On ECGs - 2014", available on Amazon.

https://www.dropbox.com/sh/l7ds8istxh4yfvy/AAA1hj1M9WxI9OxaSLwBdk1wa?dl=0&preview=0-ECG_1st_Book-GLOSSARY-(12-21.1-2014)-LOCK.pdf