अधोलोकवर्णनम् (Adholoka-varṇana) — Description of the Lower Worlds and Cosmographic Measures
तथा पञ्चदशाहानि पक्ष इत्यभिधीयते / द्वौच पक्षौभवेन्मासो द्वौमासावर्कजावृतुः
tathā pañcadaśāhāni pakṣa ityabhidhīyate / dvauca pakṣaubhavenmāso dvaumāsāvarkajāvṛtuḥ
Thus fifteen days are called a pakṣa (fortnight). Two pakṣas make a month, and two months make a solar ṛtu (season).