ṛtu: what the term means and how it is translated

Charaka SamhitaSutrasthana 6 (Tasyashitiya):Standard 6/4; Kaviratna prints his aphorism number 2 after this passage (his Lesson VI numbering runs two behind in this opening block) · checked against the source

For the purposes of this lesson, the year should be known as consisting of six portions, divided according to the seasons. Of these, the three seasons commencing with the season of dews and ending with summer constitute the period when the Sun travels in the region lying to the north of the equinoctial. That is again the period when the Sun takes (i.e., sucks up the liquid portion of every earthly object). The three other seasons commencing with the season of rains and ending with Hemanta constitutes the period of the Sun's southerly course. That is, besides, the time when the Sun gives (or yields moisture to all earthly objects).

Six ṛtus and the ādāna ('Taking') / visarga ('Giving') division. Sanskrit seen at carakasamhitaonline.com/index.php/Tasyashiteeya_Adhyaya: इह खलु संवत्सरं षडङ्गमृतुविभागेन विद्यात्। तत्रादित्यस्योदगयनमादानं च त्रीनृतूञ्छिशिरादीन् ग्रीष्मान्तान् व्यवस्येत्, वर्षादीन् पुनर्हेमन्तान्तान् दक्षिणायनं विसर्गं च॥४॥.

Sushruta SamhitaSutrasthana VI (Ritucharya):Sushruta Sutrasthana 6.6, number confirmed as printed ॥६॥ in Susrutasamhita with Dalhana, ed. Jadavji Trikamji Acharya, Nirnaya Sagar Press 2nd ed. 1931, p. 24 (the second scheme is ॥१०॥, p. 25). Bhishagratna vol. 1 (1907): p. 46 for the quoted sentence and the month table; chapter VI opens on p. 45. · checked against the source

Sanskrit as printed in Trikamji (Su.Su. 6.6, p. 24): "तत्र माघादयो द्वादश मासाः संवत्सरः, द्विमासिकमृतुं कृत्वा षड्ऋतवो भवन्ति, ते शिशिरवसन्तग्रीष्मवर्षाशरद्धेमन्ताः; तेषां तपस्तपस्यौ शिशिरः, मधुमाधवौ वसन्तः, शुचिशुक्रौ ग्रीष्मः, नभोनभस्यौ वर्षाः, इषोर्जौ शरत्, सहःसहस्यौ हेमन्त इति ॥६॥" (Haranacandra omits संवत्सरः, per the edition's own footnote.) And Su.Su. 6.10, p. 25: "इह तु वर्षाशरद्धेमन्तवसन्तग्रीष्मप्रावृषः षड्ऋतवो भवन्ति, दोषोपचयप्रकोपोपशमनिमित्तं, ते तु भाद्रपदाद्येन द्विमासिकेन व्याख्याताः; तद्यथा—भाद्रपदाश्वयुजौ वर्षाः, कार्तिकमार्गशीर्षौ शरत्, पौषमाघौ हेमन्तः, फाल्गुनचैत्रौ वसन्तः, वैशाखज्येष्ठौ ग्रीष्मः, आषाढश्रावणौ प्रावृडिति ॥१०॥" The English in the record stays as it is; it is verbatim Bhishagratna.

Sushruta's first ṛtu scheme (Su.Su. 6.6): the twelve months from Māgha are taken two to a season, giving six seasons in the order śiśira (Māgha-Phālguna), vasanta, grīṣma, varṣā, śarad, hemanta (Agrahāyaṇa-Pauṣa). The passage makes no comparison with Charaka, and none should be drawn from it: Charaka Su 6.4 likewise begins the ādāna half with śiśira. The scheme that does differ is Sushruta's own second one at 6.6-10, six seasons for doṣa accumulation reckoned from Bhādrapada, varṣā first and prāvṛṭ last, which Bhishagratna renders with 'According to some, the rainy season consists of two months known as Bhadra and Ashvina ...'.

Ashtanga HridayaSutrasthana 3 (Ritucharya):3/1-2 per ahsutrasthana.blogspot.com: मासैर्द्विसंख्यैर्माघाध्यैः क्रमात् षट् ऋतवः स्मृताः | शिशिरो अथ वसन्तश्च ग्रीष्मो वर्षशरद्हिमाः · address only, nothing quoted to check

Vagbhata's enumeration of six ṛtus of two months each starting from Māgha. Sanskrit as transcribed on a blog; not checked against a critical edition.