Moon vocabulary · counting
How the tithis are named
Each pakṣa begins at one of the two great turning points in the lunar cycle. The count starts again at one, telling you how far the Moon has traveled through that half of its monthly clock.
A reusable Sanskrit naming pattern
The name tells you which tick of the pakṣa is underway.
Most tithi names are Sanskrit ordinal numbers: words such as first, fourth, and eleventh. Because tithi is a feminine Sanskrit noun, its ordinal takes a feminine form.
For example, dvādaśa is the Sanskrit number word for twelve. In the tithi count it appears as the feminine ordinal Dvādaśī, meaning “twelfth [tithi].” In the compound number words from eleven through fourteen, the final -a changes to -ī: ekādaśa → Ekādaśī, dvādaśa → Dvādaśī, trayodaśa → Trayodaśī, and caturdaśa → Caturdaśī. The earlier tithi names use several other ordinal patterns, which the table shows.
The same names repeat in both pakṣas from one through fourteen. Add Śukla or Kṛṣṇa to say which half of the lunar month you mean: Śukla Caturthī is the fourth waxing tithi after New Moon; Kṛṣṇa Caturthī is the fourth waning tithi after Full Moon.
The complete sequence
Learn the pattern once; use it in either pakṣa.
Position fifteen is the exception to the repeating ordinal pattern: its name tells you which great turning point closes that pakṣa.