Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
expĭātrix, īcis, f. [expiator], an atoning or expiating priestess: piatrix dicebatur sacerdos, quae expiare erat solita, quam quidam … sagam, alii expiatricem vocant, Fest. s. v. piatrix, p. 213 Müll.