वा+उतो गुणवचनात्

The word गुणवचनः means what expresses quality: i.e. \words not being words formed by primitive or secondary affixes, or other words entitled to the name of sankhya or sarvanaman, or jati, or compound words, provided they are words denoting qualities and capable of being used as adjectives qualifying substantives as the word शुक्ल is, not as the word रूप, which though it expresses a quality, cannot be used as an adjective.\ (Guide to Panini). Thus from पटु 'dexterous', we have पट्वी or पटुः (without a feminine affix); so मृदुः or मृद्वी 'soft'. Why do we say 'ending in a short उ'? Observe शुचिरियं ब्राह्मणी 'this Brahmana lady is pure'. Why do we say \expressive of a quality? \ Observe आखुः 'a mouse' (both masculine and feminine).

Vart:- After the word वसु when expressive of a quality, the affix nip is employed in the feminine; in order to make the first syllable acutely accented. As, वस्वी ॥ वसु is formed by उ (Vn. I. 10) and is adyudatta because the उ is नित् ॥

Vart:- Prohibition must be stated after the word खरु, and words though ending in short उ, have conjunct consonant as penultimate. As खरुरियं ब्राह्मणी 'a Brahmani who chooses her own husband'. Similarly पाण्डु is both gender, as ण्ड् is a conjunct consonant. As पाण्डुरियं ब्राह्मणी ॥

The word Guna गुणः 'quality' has been thus defined:-

सत्वे निविशतेपैति पृथग् जातिषु दृश्यते ।
आधेयश्चाक्रियाजश्च सोऽसत्त्वप्रकृतिर्गुणः ॥,