पुमान् स्त्रिया

A word in the masculine gender, similarly spoken along with the same word, but ending with the feminine affix, becomes एकशेष and the latter is dropped.
When two words of different genders differ only in their derivative elements but not in their radical elements, that is to say, one is masculine and the other feminine because of certain affixes, the masculine only is retained and the feminine is dropped.

The governing force of the words 'vriddha' and 'yuvan,' of sutra 1.2.65, does not extend to this sutra, but the remaining portion of sutra 1.2.65 is to be read into this sutra. When a masculine word is read along with a feminine word, the feminine word is dropped and the masculine is retained, when the difference between the two words is caused only by the feminine and masculine affixes: as ब्राह्मणः + ब्राह्मणी = ब्राह्मणौ 'the Brahmana and the Brahmani'; कुक्कुटः + कुक्कुटी = कुक्कुटौ. 'the cock and hen.'

But not so in the following:- कुक्कुटः + मयूरी कुक्कुटमयूर्यौ 'the cock and the peahen.' Similarly गणकः + गणकी = गणकगणक्यौ. Here the feminine affix ङीष्, by which the word ganaki is formed from ganaka, in addition to its feminine signification, has the further signification given to it by Rule 4.1.48, पुंयोगादाख्ययाम्, meaning the "wife of" a ganaka and not a feminine ganaka; so also इन्द्रश्च इन्द्राणी चेन्द्रेन्द्राग्यौ ॥ Similarly आर्य्यः + आर्या = आर्यौ but आर्यः + आर्याणी = आर्यार्याण्यौ. Because the feminine affix in aryani conveys more than its feminine signification. See Rule 4.1.49.

This rule does not, of course, apply when it is not a masculine noun which is compounded, but it is a noun without any gender or neuter noun which is compounded with a feminine noun. Therefore प्राक् + प्राची = प्राक्प्राच्यौ. The word प्राक् is an indeclinable and is without any gender.