a suffix occurring in loanwords from Latin, where it formed feminine nouns or adjectives corresponding to agent nouns ending in -tor, (Bellatrix). On this model, -trix, is used in English to form feminine nouns (aviatrix; executrix) and geometrical terms denoting straight lines (directrix).
Usage note A suffix borrowed directly from Latin, -trix has been used since the 15th century on feminine agent nouns that correspond to a masculine (in Latin) or generic (in English) agent noun ending in -tor:aviator, aviatrix; legislator, legislatrix; orator, oratrix. Most nouns in -trix have dropped from general use, so that terms like aviatrix, benefactrix, legislatrix, oratrix, and proprietrix occur rarely or not at all in present-day English. The forms in -tor are applied to both men and women: Her sister is the proprietor of a new restaurant. When relevant, sex is specified with the generic term: Amelia Earhart was a pioneer woman aviator. Legal documents still use administratrix, executrix, inheritrix, and the like, but these forms too are giving way to the -tor forms. See also -enne, -ess, -ette.