An Etymological Dictionary of Astronomy and Astrophysics

1. The number of days that have elapsed since the last → conjunction of the Sun and Moon. It is 7 days at → first quarter, 15 days at → full moon, and 22 days at → third quarter.
   

2. The time past since the → formation of the Moon.

Etymology (EN): → Moon; → age.

Etymology (PE): 1) Kohan-ruzi literally “age in days,” from kohan-ruz “old in days,” from kohan “old, ancient,” kohné “worn;”
Mid.Pers. kahwan “old, aged, worn;”
pir; Mid.Pers. pir “old, aged, ancient;” Av. parô (adv.) “before, before (of time),” in front (of space); cf. Skt. puáh, combining form of puras “before (of time and place), in front, in advance;” mâh, → Moon.
2) Senn, → age.