-trixsuff.1. A female that is connected with a specified thing: testatrix.2. A geometric point, line, or surface: directrix.[Middle English, from Latin -tr?x, feminine of -tor, n. suff.]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.-trix suffix forming nouns indicating a feminine agent, corresponding to nouns ending in -tor: executrix. [from Latin]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014-trix a suffix occurring in loanwords from Latin, where it formed feminine nouns or adjectives corresponding to agent nouns ending in -tor; on this model, -trix is used in English to form feminine nouns (aviatrix; executrix) and geometrical terms denoting straight lines (directrix). Also, -trice.[